refactor(frontend): extract useQuickTemplates from TerminalView.vue

[attson]

Summary

Second slice of milestone 5-b. Templates state (list + hidden flag + pending-confirm) and every function that manipulates them (`sendTemplate`, `requestTemplateSend`, `confirmTemplateSend`, `cancelTemplateSend`, `onTemplateHotkey`, `onTemplateBarWheel`) plus the `parseHotkey`/`hotkeyMatches` internals were interleaved with the rest of TerminalView.vue's setup.

Move to `composables/useQuickTemplates.ts`. The composable takes:
```ts
{ send, confirmRequired, focused, templatesBridge }
```
where `send` is the closure that wraps `conn?.sendInput` so the composable stays session-transport agnostic — critical because that's where the two-writes-per-template split lives.

⚠️ HARD CONSTRAINT preserved inline in `sendTemplate`

```ts
send(tpl.text);
window.setTimeout(() => send("\r"), 16);
```

This must NOT be "simplified" into a single `sendInput` call — Codex and other raw-mode TUIs treat bundled `"text\r"` as a paste (the CR becomes a literal newline in the prompt instead of submitting). Regressed twice before: fixed in #63, deleted in #110, re-fixed in #129. Documented in memory as `[[feedback_template_send_split_cr]]`.

TerminalView side

• Drop `templates` / `templatesHidden` / `pendingTemplateConfirm` refs (moved).
• Drop `templateConfirmOpen` computed (composable exports it).
• Drop `templateConfirmRequired` computed (passed in as `confirmRequired` arg).
• Drop `sendTemplate` / `requestTemplateSend` / `cancelTemplateSend` / `confirmTemplateSend` / `onTemplateHotkey` / `onTemplateBarWheel` functions.
• Drop `parseHotkey` + `hotkeyMatches` helpers (private to composable now).
• Drop `effectiveTemplates` import (consumed by composable).
• Add `useQuickTemplates` destructure + composable import.
• `reloadShortcutBars` simplifies: delegates templates to `reloadQuickTemplates()` and reloads aux keys inline (aux keys stay here until M5-b-5 extracts TerminalAuxKeyBar).

Test update

Two source-scan tests in `TerminalView.test.ts` that pinned the exact old inline structure now also scan `useQuickTemplates.ts?raw` for the moved parts. Regex tweaked to match the composable's 2-space-indented nested-function closing braces.

Net: TerminalView.vue -110 / +21 (net -89, 2724 → 2635); new composable +181.

Test plan

• `npm test` 1631/1631
• `npm run build` (vue-tsc + vite) green
• Manual (desktop): tap a template button in the mobile shortcut bar → text + Enter sent as two writes (Codex prompt submits, not pastes)
• Manual (web): first tap opens confirm panel; second tap sends
• Manual: template hotkey (e.g. Mod+1) fires on the focused pane only