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/semantic_memory.py

@@ -16,9 +16,8 @@ import json
 import logging
 import sqlite3
 from dataclasses import dataclass
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 from pathlib import Path
-from typing import Optional
 
 logger = logging.getLogger(__name__)
 
@@ -84,7 +83,7 @@ def cosine_similarity(a: list[float], b: list[float]) -> float:
     """Calculate cosine similarity between two vectors."""
     import math
 
-    dot = sum(x * y for x, y in zip(a, b))
+    dot = sum(x * y for x, y in zip(a, b, strict=False))
     mag_a = math.sqrt(sum(x * x for x in a))
     mag_b = math.sqrt(sum(x * x for x in b))
     if mag_a == 0 or mag_b == 0:
@@ -154,7 +153,7 @@ class SemanticMemory:
         chunks = self._split_into_chunks(content)
 
         # Index each chunk
-        now = datetime.now(timezone.utc).isoformat()
+        now = datetime.now(UTC).isoformat()
         for i, chunk_text in enumerate(chunks):
             if len(chunk_text.strip()) < 20:  # Skip tiny chunks
                 continue