refactor(web): delete dead code (R2) — 1736 lines removed

Tool-renderer registry (21 files, ~1.5k lines):
- src/lib/tool-renderers.ts — registry + getToolRenderer (exported, never
  imported anywhere)
- src/lib/renderers/index.ts + 10 .ts registrars + 10 .svelte components
- main.ts: removed the requestAnimationFrame(() => import('./lib/renderers'))
  that was the only thing keeping the dead subsystem alive

Dead components (never imported):
- ToolCallGroup, PlanProgress, GoalHeader, InlineApproval, SessionDigest

Dead store exports (written, never read):
- context.ts: pendingApprovals writable (+ Approval type import)
- events.ts: connectionState writable (+ its .set() calls)

Dead API surface:
- api.ts: SessionDigest interface + fetchSessionDigest (only caller was the
  dead SessionDigest.svelte)

Dead npm deps:
- mode-watcher (0 imports; superseded by stores/theme.svelte.ts)
- @internationalized/date (0 imports)

Also: fix stale comments referencing deleted symbols, update plan R1/R2
status. Build clean (4683 modules, down from 4706; one Svelte 5 warning
gone — the dead HealthSummary.svelte was emitting state_referenced_locally).

web/package.json

@@ -12,14 +12,12 @@
     "lint": "svelte-check --tsconfig ./tsconfig.json"
   },
   "devDependencies": {
-    "@internationalized/date": "^3.12.2",
     "@lucide/svelte": "^1.23.0",
     "@sveltejs/vite-plugin-svelte": "^5.0.0",
     "@tailwindcss/vite": "^4.3.2",
     "@tsconfig/svelte": "^5.0.0",
     "@types/d3-force": "^3.0.10",
     "bits-ui": "^2.18.1",
-    "mode-watcher": "^1.1.0",
     "svelte": "^5.0.0",
     "svelte-check": "^4.0.0",
     "svelte-sonner": "^1.1.1",