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- mode-watcher (0 imports; superseded by stores/theme.svelte.ts)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/src/lib/api.ts

@@ -351,21 +351,6 @@ export async function fetchRecentActivity(limit = 50): Promise<ActivityItem[]> {
   return data.items ?? []
 }
 
-export interface SessionDigest {
-  session_id: string
-  total_executions: number
-  by_status: Record<string, number>
-  entities_touched: string[]
-  executions: { target: string; verb: string; summary: string; risk_class: string; status: string }[]
-  knowledge_created: string[]
-}
-
-export async function fetchSessionDigest(sessionId: string): Promise<SessionDigest | null> {
-  const res = await fetchWithAuth(`${API}/activity/session/${sessionId}`)
-  if (!res.ok) return null
-  return res.json()
-}
-
 export interface CapabilityTimelineItem {
   verb: string
   first_success: string | null