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/map-limits.ts

@@ -47,6 +47,15 @@ export const MAX_TODOS_PER_SESSION = 500;
 // Pending Tool Calls Limits
 // ============================================================================
 
+// ============================================================================
+// Agent Tracking Limits
+// ============================================================================
+
+/**
+ * Maximum agents to track across all sessions (LRU eviction when exceeded).
+ */
+export const MAX_TRACKED_AGENTS = 500;
+
 /**
  * Maximum pending tool calls to track per subagent.
  * Entries should be cleaned up on tool_result, but this prevents leaks.