refactor: consolidate ~70 scattered constants into 6 new config files (phase 6)

Create 6 domain-focused config files in src/config/ to centralize operational
tuning knobs that were scattered across 15+ source files:

- server-timing.ts: SSE batching, state debounce, scheduled runs, error recovery
- auth-config.ts: session TTL, rate limits, hook timeout
- tunnel-config.ts: QR token rotation, tunnel process lifecycle
- terminal-limits.ts: input length, terminal cols/rows, session name
- ai-defaults.ts: AI model string, idle/plan context limits
- team-config.ts: poll interval, cache sizes

Eliminates all cross-file duplicates:
- AI model string: 5 occurrences → 1 (config only)
- STATS_COLLECTION_INTERVAL_MS: 2 → 1
- timeout: 10000 in hooks-config: 6 → 0 (now HOOK_TIMEOUT_MS)
- MAX_TRACKED_AGENTS shadow: removed, imports from map-limits

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/config/ai-defaults.ts

@@ -0,0 +1,18 @@
+/**
+ * @fileoverview Default model and context limits for AI-powered checkers.
+ *
+ * Centralizes the AI model identifier and context window sizes used by
+ * the idle checker, plan checker, respawn controller defaults, and
+ * respawn route fallbacks. Change the model here when upgrading.
+ *
+ * @module config/ai-defaults
+ */
+
+/** Default model for AI idle and plan checkers */
+export const AI_CHECK_MODEL = 'claude-opus-4-5-20251101';
+
+/** Max context chars for idle checker (~4k tokens) */
+export const AI_IDLE_CHECK_MAX_CONTEXT = 16000;
+
+/** Max context chars for plan checker (~2k tokens, plan mode UI is compact) */
+export const AI_PLAN_CHECK_MAX_CONTEXT = 8000;