T-235: TerminalGrid.tsx — 1-4 panes responsive layout + add/close + i18n keys

[mpiton]

Goal

src/features/terminals/TerminalGrid.tsx: responsive grid that lays out 1-4 <Terminal /> panes (CSS Grid repeat(auto-fit, minmax(...))) with an "Add terminal" tab button and per-pane close button. Reads useTerminalsStore. No state of its own beyond layout.

Layout rules:

• 1 terminal → fullscreen pane
• 2 terminals → split horizontal
• 3 terminals → 2-1 stack
• 4 terminals → 2×2 grid
• 5+ → guard rail: button disabled, toast "Max 4 terminals (configurable in Settings, future sprint)"

Per ARCHI §11.5: limit configurable later via AppSettings. Hard-coded 4 cap here, follow-up issue tracks dynamic limit.

Acceptance criteria

• Grid component renders correct layout for 1/2/3/4 panes (snapshot tests)
• "Add terminal" button calls useTerminalsStore.open({ project_id, cols: 100, rows: 32 }); disabled at cap
• Per-pane "X" button calls useTerminalsStore.close(id)
• Focused terminal has visible ring (Tailwind ring-2 ring-primary)
• Tab-key cycles focus between panes
• i18n strings added to src/shared/i18n/locales/{en,fr}.json (T-222 parity test must stay green):
  • terminals.add / terminals.close / terminals.exited / terminals.maxReached
• Unit tests:
  • it("should render 4 grid panes when 4 terminals are open")
  • it("should disable add button when 4 terminals are open")
  • it("should call close on store when close button clicked")
• pnpm exec oxlint . --max-warnings=0 clean; vitest snapshots regenerated

Files to create/modify

• create src/features/terminals/TerminalGrid.tsx
• create src/features/terminals/TerminalGrid.test.tsx
• modify src/shared/i18n/locales/en.json
• modify src/shared/i18n/locales/fr.json
• modify src/App.tsx to add a /terminals route or expose grid where appropriate

References

• PRD.md F-003 + F-082 sortable terminal cards
• ARCHI.md §6.5
• T-222 i18n parity invariant

Dependencies

Blocked by T-234.