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/tunnel-config.ts

@@ -0,0 +1,44 @@
+/**
+ * @fileoverview Cloudflare tunnel and QR authentication constants.
+ *
+ * Controls QR token rotation timing, rate limiting,
+ * and tunnel process lifecycle.
+ *
+ * @module config/tunnel-config
+ */
+
+// ============================================================================
+// QR Token Rotation
+// ============================================================================
+
+/** QR token auto-rotation interval (ms) */
+export const QR_TOKEN_TTL_MS = 60_000;
+
+/** Grace period — previous token still valid during rotation (ms) */
+export const QR_TOKEN_GRACE_MS = 90_000;
+
+/** Length of the short code in QR URL path (chars) */
+export const SHORT_CODE_LENGTH = 6;
+
+// ============================================================================
+// QR Rate Limiting
+// ============================================================================
+
+/** Global rate limit for QR auth attempts across all IPs */
+export const QR_RATE_LIMIT_MAX = 30;
+
+/** QR rate limit reset window (ms) */
+export const QR_RATE_LIMIT_WINDOW_MS = 60_000;
+
+// ============================================================================
+// Tunnel Process Lifecycle
+// ============================================================================
+
+/** Max time to wait for cloudflared URL before timeout (ms) */
+export const URL_TIMEOUT_MS = 30_000;
+
+/** Restart delay after unexpected tunnel exit (ms) */
+export const RESTART_DELAY_MS = 5_000;
+
+/** SIGTERM → SIGKILL escalation timeout (ms) */
+export const FORCE_KILL_MS = 5_000;