Make w7-flat actually flatten; document this round

The status bar's transfers summary is a text toggle, but 7.css painted it as
a full Aero push button — a stray bordered slab sitting in the status line.
Marked it w7-flat, the per-button escape hatch that existed for exactly this
and had never been used.

It did not work, for a reason worth keeping: 7.css restates border-color at
`.win7 button:not(:disabled):not(:hover)` = (0,3,1), which outranks
`.win7 .w7-flat` = (0,2,0). The .w7-toolbar arm of the same rule only ever
won that fight by tying on specificity and landing later in the same layer —
an accident w7-flat did not share. Split the rule: `background:
revert-layer` stays in `skin` (it must land on `utilities`), and the
paint-suppression literals move to `skinfix`, where layer order settles it
instead of a specificity arms race.

Docs updated in the same change per the working agreement — architecture.md
gains the tabs contract, the w7-flat/w7-toolbar split and the frame
transparency invariant; gotchas.md gains a win7-skin section (unlayered beats
every layer, the (0,3,1) border-color restatement, overflow-x clipping the
y-axis, 7.css's hardcoded light literals, exact selectors) plus the two
Angular traps this round hit: a duplicate `class` attribute is silently
dropped, and a backtick inside a component template's HTML comment terminates
the TS template literal.

Also recorded the verification trap that cost three wrong readings today:
`bun run start` leaves the old instance running and `import -window` grabs
the OLDEST match, so screenshots silently come from a stale build — this is
what made the w7-flat fix above look like a no-op when it was already
correct. Kill and count instances before capturing. And `pkill -f
'electrobun dev'` matches the shell running it and kills your own command.

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

docs/architecture.md

@@ -307,8 +307,37 @@ still scales and 7.css's `pt` shorthand stops resetting weight/line-height.
 **Markup hooks**: `role="progressbar"` (+aria) on the transfer bars,
 `has-scrollbar` on scroll containers (7.css only styles `::-webkit-scrollbar`
 under that class), `w7-toolbar` on the three header rows (their buttons go
-flat — Explorer's command bar was flat, unlike dialog push buttons), `w7-btn`
-on the 10 dialog action buttons.
+flat — Explorer's command bar was flat, unlike dialog push buttons), `w7-flat`
+as the per-button escape hatch for the same treatment outside a toolbar (the
+status-bar transfers summary is a text toggle, not a push button), `w7-btn`
+on the 10 dialog action buttons. The flat treatment is split across two
+layers on purpose: `background: revert-layer` must sit in `skin` to reach
+`utilities`, while `border-color`/`box-shadow` sit in `skinfix` because 7.css
+restates `border-color` at (0,3,1) and no sane `.w7-flat` selector outranks
+that.
+
+**Tabs**: the workspace strip is 7.css's real tab component —
+`menu[role=tablist]` + one `button[role=tab][aria-selected]` per workspace, so
+the framework draws the joined inactive tabs and the raised active one. The
+selector is a DESCENDANT (`menu[role=tablist] button`), so the `+` button, the
+update pill and the right-hand tools deliberately sit outside the `<menu>`.
+Tabs are exempted from the `w7-toolbar` flattening via `:not([role='tab'])` —
+they want the full Aero slab their neighbours are stripped of. There is no
+per-tab ✕ (Win7 tab controls had none, and a nested button is invalid HTML):
+closing is `Ctrl/Cmd+W` or middle-click. `role="tabpanel"` on the panel area
+was considered and rejected — its `padding: 14px`, `margin-bottom: 9px` and
+border fight the split-pane layout for a join that cannot read anyway with the
+panel toolbar row in between.
+
+**Frame transparency**: the rounded frame only reads as rounded because
+nothing paints an opaque full-bleed ground behind it. That is not free —
+`html, body` paint `var(--background)` **unlayered**, which beats every
+`@layer`, so `.win7` resets them to transparent in an equally unlayered rule
+next to the `font-family` one. A maximized window drops the radius (7.css
+declares it three times: `.window`, `::before`, `::after` — all three must be
+zeroed); the frame reads the state off its own child with
+`:has(> .title-bar.is-maximized)`, which `title-bar.ts` publishes from its
+existing `maximized` signal rather than subscribing to `windowState` twice.
 
 **Context menu**: pure 7.css via its real menu contract —
 `ul[role=menu] > li[role=menuitem] > button` for actions,