Scale stage 3: shortcuts service + Ctrl/Cmd +/-/0 for the scale

Groundwork for the vim-style bindings planned next: the app previously had NO
keyboard abstraction — `event.metaKey || event.ctrlKey` copy-pasted inline in
six places, no typing-target guard anywhere, every window root matching keys
by hand.

New @core/shortcuts.service.ts owns:
- isMod() (also accepts MouseEvent — Mod+click toggle-select uses the same
  rule) and isTypingTarget();
- ONE declarative keymap: resolve(event, scope) -> ShortcutId | null, scoped
  main / editor / manager. Layout rules are encoded once: digits, +/- and
  Alt-letter chords match on event.code (AZERTY digit rows, layouts where '+'
  needs Shift, macOS Option-Z producing Ω); plain letter chords match on
  event.key so they follow the user's layout.

Both app.ts, both editor-window.ts and both connection-manager.ts now resolve
through the service and switch on ids — behaviour-preserving for every
existing shortcut, including the deliberate quirks (Ctrl+Tab never meta
because Cmd-Tab is the macOS app switcher; Cmd+9 = last tab; editor Mod+W is
the Windows/Linux arm, macOS routes via the app menu). Escape and Tab stay
component-local on purpose: their meaning is per-window state (find bar open?
close prompt up? caret in the textarea?), not a global binding. The file
panels keep their contextual key state machine but delegate modifier tests.

On top of the table: Ctrl/Cmd +/-/0 steps/resets the interface scale in every
window kind, all three previously unclaimed. isTypingTarget is applied
per-shortcut, not globally in resolve(): the scale keys must not fire while
typing ('-' in a rename prompt must type '-'), but the editor WANTS Mod+S
mid-typing and the tab shortcuts keep their existing reach.

Docs: architecture.md's density prose now describes the uiScale lever;
gotchas.md gains the scale section — the disassembly evidence that native
page zoom is an empty stub on Linux (so nobody tries it again), the
everything-must-be-rem rule, the skinfix-outranks-variants trap the harness
caught (48px close button silently 29px), and the px-mirrors-in-TS class of
bug with the remPx() remedy.

Verified: tsc + build clean; live boot with the user's real legacy settings
file migrates textSize:large -> uiScale 1.2 and renders scaled. Not verified
here (needs interaction): the stepper clicks and the shortcut keys themselves.

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

docs/architecture.md

@@ -305,9 +305,15 @@ toolbars deliberately stay on `--background`. Accent tones: one
 `@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. Text-size levels set `--row-h`,
-`--list-font` etc. per `data-text` attribute, consumed via `h-(--row-h)` /
-`text-(length:--list-font)` arbitrary utilities.
+pixel-identical to the old neutral hover. **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, `--w7-fs`
+and the 7.css bridge in 7like.css), both skins scale whole, chrome included.
+Driven by the tab-bar stepper, Ctrl/Cmd +/−/0, and preload-baked for a
+flash-free first paint. It replaced the 3-tier `data-text` axis; the store
+migrates old `textSize` values. TS that measures rem-sized CSS converts through
+`@core/metrics` `remPx()` — never an assumed 16.
 
 ### Skins (`settings.skin`: `modern | win7`)
 
@@ -335,7 +341,7 @@ main window still ran the old one.
 
 **Stylesheet split.** `ui/src/styles.css` holds only what BOTH skins consume —
 the `@layer` statement, the Tailwind import, OKLCH tokens, `@theme inline`,
-`data-text` sizes, animations, the accent axis, and the `html, body` base. Each
+panel-chrome tokens, animations, the accent axis, and the `html, body` base. Each
 skin's own rules live in its folder (`skins/7like/7like.css`,
 `skins/shadlike/shadlike.css`) and are `@import`ed from there. `shadlike.css` is
 near-empty by nature: that skin IS the shared token system plus inline Tailwind.
@@ -368,8 +374,10 @@ right too. It adds NO new tokens on purpose — a new colour would need another
 `:root.win7[data-accent]` feeds it to `--w7-w-bg`, which is authentic (Win7
 shipped "Window Color"). Dark Win7 is hand-authored (Microsoft never shipped
 one) as ~20 `--w7-*` overrides, duplicated forced + system like every other
-dark block. `--w7-font` is restated as a px `font` shorthand so `data-text`
-still scales and 7.css's `pt` shorthand stops resetting weight/line-height.
+dark block. `--w7-font` is restated as a rem `font` shorthand so the interface
+scale reaches it and 7.css's `pt` shorthand stops resetting weight/line-height;
+the rest of 7.css's px metrics are re-expressed in rem by the scale bridge in
+7like.css's `skinfix`.
 
 **Markup hooks**: `role="progressbar"` (+aria) on the transfer bars,
 `has-scrollbar` on scroll containers (7.css only styles `::-webkit-scrollbar`