feat(dsh-plugin-browserskill): reskin the overlay with BrowserSkill's own UI system

The previous pass aligned the observation overlay with the dsh shell; the
product call is the opposite direction — the floating card should read as a
BrowserSkill surface, not a shell-native widget.

- Reuse @browser-skill/ui directly (Button, cn); status dots spec'd after the
  extension popup's ConnectionStatusIndicator; Remix icons for
  interrupt/pin/warn/pop-out.
- Compile the BSK tailwind utility sheet scoped under the .bsk-obs root class
  (scripts/build-client-css.mjs + postcss-prefix-selector) and ship the oklch
  design tokens on the same scope, so nothing leaks into the host shell and
  the shell theme cannot bleed back. tsdown injects .nomodule.css verbatim
  (minified, unhashed) alongside the hashed CSS modules.
- BSK ships no shared tooltip, so the one-time interrupt semantics hint is a
  card-spec bubble (bg-card/border/12px radius), retired after first use.
- Tests: pin react/react-dom to this package's 18.x copies in vitest — the ui
  package sources peer on react ^19 and would otherwise emit react-19
  (transitional) elements that the react-18 renderer rejects. Production is
  unaffected (react stays external, provided by the shell).
- stylelint: ignore the generated bsk-ui.nomodule.css.

packages/dsh-plugin-browserskill/README.md

@@ -76,8 +76,13 @@ All fields are optional and validated through the plugin's Schemastery `Config`:
 When the plugin runs inside the dsh Web UI, an **observation overlay** floats over the app
 (registered into the `shell.overlay` seat): a breathing thumbnail per owned session plus its
 current action and elapsed time. The card docks at the top-right of the content area (clear of
-the composer and the shell's header controls) and follows the shell's own visual language —
-shared `ui-primitives` controls and `--dsw-alias-*` semantic tokens throughout.
+the composer and the shell's header controls) and wears the **BrowserSkill product family's own
+look**: the overlay reuses `@browser-skill/ui` components (`Button`, `cn`) and its oklch design
+tokens (`--card`, `--primary`, `--destructive`, `--ring`, …), status dots spec'd after the
+extension popup's connection indicator, and Remix icons. The BSK utility sheet is compiled
+scoped under the `.bsk-obs` root class (`scripts/build-client-css.mjs`), so the overlay looks
+like the BrowserSkill extension without leaking a single selector into the host shell — and the
+shell's theme cannot bleed back in.
 
 - **Lifecycle**: hidden while the plugin owns no sessions; appears on the first
   `browser_session_start`; disappears when all sessions stop (or the plugin unloads).