ruff (#169)

* polish: streamline nav, extract inline styles, improve tablet UX

- Restructure desktop nav from 8+ flat links + overflow dropdown into
  5 grouped dropdowns (Core, Agents, Intel, System, More) matching
  the mobile menu structure to reduce decision fatigue
- Extract all inline styles from mission_control.html and base.html
  notification elements into mission-control.css with semantic classes
- Replace JS-built innerHTML with secure DOM construction in
  notification loader and chat history
- Add CONNECTING state to connection indicator (amber) instead of
  showing OFFLINE before WebSocket connects
- Add tablet breakpoint (1024px) with larger touch targets for
  Apple Pencil / stylus use and safe-area padding for iPad toolbar
- Add active-link highlighting in desktop dropdown menus
- Rename "Mission Control" page title to "System Overview" to
  disambiguate from the chat home page
- Add "Home — Timmy Time" page title to index.html

https://claude.ai/code/session_015uPUoKyYa8M2UAcyk5Gt6h

* fix(security): move auth-gate credentials to environment variables

Hardcoded username, password, and HMAC secret in auth-gate.py replaced
with os.environ lookups. Startup now refuses to run if any variable is
unset. Added AUTH_GATE_SECRET/USER/PASS to .env.example.

https://claude.ai/code/session_015uPUoKyYa8M2UAcyk5Gt6h

* refactor(tooling): migrate from black+isort+bandit to ruff

Replace three separate linting/formatting tools with a single ruff
invocation. Updates tox.ini (lint, format, pre-push, pre-commit envs),
.pre-commit-config.yaml, and CI workflow. Fixes all ruff errors
including unused imports, missing raise-from, and undefined names.
Ruff config maps existing bandit skips to equivalent S-rules.

https://claude.ai/code/session_015uPUoKyYa8M2UAcyk5Gt6h

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/timmy/tools_intro/__init__.py

@@ -7,7 +7,7 @@ being told about it in the system prompt.
 import logging
 import platform
 import sys
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 from pathlib import Path
 from typing import Any
 
@@ -281,7 +281,7 @@ def get_live_system_status() -> dict[str, Any]:
     try:
         from dashboard.routes.health import _START_TIME
 
-        uptime = (datetime.now(timezone.utc) - _START_TIME).total_seconds()
+        uptime = (datetime.now(UTC) - _START_TIME).total_seconds()
         result["uptime_seconds"] = int(uptime)
     except Exception:
         result["uptime_seconds"] = None
@@ -294,5 +294,5 @@ def get_live_system_status() -> dict[str, Any]:
     except Exception:
         result["discord"] = {"state": "unknown"}
 
-    result["timestamp"] = datetime.now(timezone.utc).isoformat()
+    result["timestamp"] = datetime.now(UTC).isoformat()
     return result