Adopt Oxide's color scheme and a square design

The palette now follows Oxide's design system (docs.oxide.computer): a cool
neutral scale at hue 260 with almost no chroma, opaque strokes, and Oxide's
green as the only accent. The accent-color option is gone: selection, the
cursor row, focus rings and the active-panel line all read green.

The file panel's header strip now steps toward the list, one shade per row
(session strip, path bar, column headers), derived by color-mix so every
theme, AMOLED included, follows on its own.

Everything is square: every rounded utility and the radius tokens are gone,
and checkboxes, radios, selects, number spinners and scrollbars are
restyled to match (square scrollbars are always visible on macOS, the cost
of styling them).

Co-Authored-By: Claude <noreply@anthropic.com>

docs/architecture.md

@@ -49,8 +49,7 @@ before any page script, plus the persisted theme attributes and interface
 scale so the first paint is already right. `ui/src/main.ts` picks the root
 component from `APP_MODE`; all four roots use selector `app-root` (index.html
 hosts only that tag). `chromeOptions()` is the ONLY place the native frame is
-decided, spread by
-the main window and `openSecondaryWindow`: macOS `hiddenInset` +
+decided, spread by the main window and `openSecondaryWindow`: macOS `hiddenInset` +
 `trafficLightOffset {x:12,y:13}` (the UI renders an `h-10 pl-24` drag-region
 header via `IS_MAC_CHROME`); other platforms keep the native titlebar and a
 compact `h-9` non-drag header.
@@ -233,7 +232,7 @@ component; tokens → `ui/src/styles.css`.
   enqueue and runs the collision flow (same-path auto-skip, type-mismatch
   skip, overwrite dialog with all/none batch modes).
 - `settings.service.ts` — one signal per setting; **imperative apply pattern**
-  (`applyTheme/DarkTone/Accent` set `data-*` attributes on `<html>`;
+  (`applyTheme/DarkTone` set `data-*` attributes on `<html>`;
   `applyUiScale` sets its inline `font-size`); `applyAll` also serves the
   `settingsChanged` broadcast, so every window follows a save made in any
   other. Every window RPC serves `saveSettings` (editor and manager windows
@@ -281,7 +280,7 @@ component; tokens → `ui/src/styles.css`.
   pointer; the keyboard path never consults it — so `pick()` and the arrow-key
   walker check the flag themselves.
 - `file-icons.ts` — extension → category map driving glyphs, colors
-  (fixed `--icon-*` tokens, never accent-tinted) and the Kind column.
+  (fixed `--icon-*` tokens from Oxide's hue scales) and the Kind column.
 - `icons.ts` — the one icon registry (TDesign, `@ng-icons/tdesign-icons`), passed to
   `provideIcons` in `app.config.ts`. Icon names are plain strings in templates and
   the build never checks them: an unregistered name renders nothing (console error
@@ -301,35 +300,42 @@ component; tokens → `ui/src/styles.css`.
 
 ## Theming
 
-`ui/src/styles.css`: shadcn-style OKLCH tokens; dark values are duplicated in
-`:root[data-theme='dark']` AND a `prefers-color-scheme` media block (system
-mode) — every dark token change goes in BOTH. Light is the zinc family; the
-dark neutrals are a **warm gray family (hue 107)** anchored on `#1a1a19`
-(`--background`) — retoning one dark neutral means retoning them all, or warm
-and cool surfaces clash. **Surface layers**, each its own shade: `--chrome`
-(frame — tab/transfer/status bars, editor/manager header+footer strips, the
-manager's connection sidebar), `--toolbar` (each file panel's header strip —
-session strip, path bar, column headers — and the editor's search bar; both
-panels share one neutral strip, and the ACTIVE panel is marked by a 0.125rem
-`--primary` line along its top edge, an inset box-shadow on the session strip so
-switching panels never shifts layout), `--background` (file lists, editor
-text, forms; `--row-alt` stripes odd file rows, skipped on the cursor/selected
-row so two `bg-*` utilities never fight) and `--card` (popovers, dialogs,
-toasts). Dark climbs frame 0.165 < list 0.218 < header 0.265 < card 0.285;
-light steps greys out from white content: frame 0.935 < header 0.965 < list =
-card 1. **`--accent` is translucent** (6% zinc-900 light, 9% white dark):
-hover/selected states sit on every layer, and an opaque hover vanishes on a
-surface of its own lightness. The "darker" tone is true-black AMOLED: chrome,
-background, toolbar and row-alt are all `#000` (the layers collapse
-on purpose), elevation survives only via `--card`/`--accent` (opaque there),
-and `--border`/`--input` go to 16%/18% white because those lines then carry the
-whole layout. Accent tones: one
-`--tone-h/--tone-c` line per tone + three formula blocks derive `--primary`,
-`--ring`, `--cursor-tint`; graphite = attribute removed = pristine zinc.
+`ui/src/styles.css`: OKLCH tokens adapted from **Oxide's design system**
+(docs.oxide.computer: a cool neutral scale at hue 260 with almost no chroma,
+one green accent, opaque strokes; the comments carry Oxide's step names
+n0…n1300 / green-800). Dark values are duplicated in `:root[data-theme='dark']`
+AND a `prefers-color-scheme` media block (system mode) — every dark token
+change goes in BOTH; retone neutrals along the one scale, or warm and cool
+surfaces clash. **There is no accent setting**: `--primary` is Oxide green per
+theme (green-800 dark, green-500 light), so selection (`bg-primary/15`), the
+cursor row (`--cursor-tint`, a `color-mix` of `--primary`), focus rings
+(green-600) and `--success` all read green. **Surface layers**, each its own
+shade: `--chrome` (frame — tab/transfer/status bars, the editor/manager/settings
+header+footer strips and sidebars), the file panel's header strip **stepping
+toward the list** — session strip `--toolbar`, path bar `--toolbar-2`, column
+headers `--toolbar-3` (`color-mix` steps declared once in `:root`, so every
+theme follows) — then `--background` (file lists, editor text, forms;
+`--row-alt` stripes odd file rows, skipped on the cursor/selected row so two
+`bg-*` utilities never fight) and `--card` (popovers, dialogs, toasts). The
+ACTIVE panel is marked by a 0.125rem `--primary` line along its top edge (an
+inset box-shadow on the session strip, so switching panels never shifts
+layout). Dark: frame 0.162 < list 0.195 < header 0.275 → 0.248 → 0.221 < card
+0.29; light steps greys out from near-white content: frame 0.925 < header 0.95
+→ 0.965 → 0.98 < list = card 0.995. **`--accent` is translucent** (n0 at 5%
+light, white 7% dark): hover/selected states sit on every layer, and an opaque
+hover vanishes on a surface of its own lightness. Strokes are opaque
+(`--border` n300 dark / n900 light, `--input` one step stronger). The
+"darker" tone is true-black AMOLED: chrome, background, toolbar (+ its steps)
+and row-alt are all `#000` (the layers collapse on purpose); elevation
+survives only via `--card`/`--muted`/`--accent` (opaque there). **Square
+design**: no `rounded-*` utilities and no radius tokens; an `@layer base`
+block restyles native controls to match — checkboxes/radios (`appearance:
+none`, a drawn check / square dot), selects (a `currentColor` caret; use
+`pl-*`, never `px-*`, on a select), hidden number spinners, and square
+`::-webkit-scrollbar`s (which make macOS scrollbars always visible).
 `@theme inline` maps tokens to Tailwind utilities (`bg-primary`,
-`text-icon-folder`, `bg-cursor-tint`). Selected rows are `bg-primary/15`
-(follow the accent); the cursor row uses `--cursor-tint` so graphite stays
-pixel-identical to the old neutral hover. **Interface scale** (`settings.uiScale`,
+`text-icon-folder`, `bg-toolbar-2`, `bg-cursor-tint`). File-type icon colors
+come from Oxide's hue scales (800 steps dark, 600 light). **Interface scale** (`settings.uiScale`,
 0.5–4 in 0.1 steps): one root font-size lever — `applyUiScale` sets
 `html { font-size: 16px * scale }`, and since EVERY size in the app is rem
 (panel tokens like `--row-h`, all Tailwind utilities, ng-icon sizes), the