Split webui into Flask blueprints and data domain modules

- Split app.py (66 routes) into 3 blueprints: pages (public), api (JSON), admin (@admin_required)
- Split data.py (4,360 LOC) into 7 domain modules: drafts, authors, ratings, gaps, analysis, search, proposals
- Add data/__init__.py re-exporting all public functions for backward compatibility
- Add custom 404/500 error pages matching dark theme
- Add request timing logging via before_request/after_request hooks
- Refactor app.py into create_app() factory pattern
- All 106 tests pass, all 66 routes preserved

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

src/webui/data/_shared.py

@@ -0,0 +1,46 @@
+"""Shared utilities for webui data modules."""
+from __future__ import annotations
+
+import sys
+import time
+from pathlib import Path
+
+# Ensure project src is on path
+_project_root = Path(__file__).resolve().parent.parent.parent.parent
+if str(_project_root) not in sys.path:
+    sys.path.insert(0, str(_project_root / "src"))
+
+from ietf_analyzer.config import Config
+from ietf_analyzer.db import Database
+from ietf_analyzer.readiness import compute_readiness, compute_readiness_batch
+
+# Simple TTL cache for expensive computations (t-SNE, clustering, similarity)
+_cache: dict[str, tuple[float, object]] = {}
+_CACHE_TTL = 300  # 5 minutes
+
+
+def _extract_month(time_str: str | None) -> str:
+    """Normalize a date string to YYYY-MM format."""
+    if not time_str:
+        return "unknown"
+    if len(time_str) >= 7 and time_str[4] == '-':
+        return time_str[:7]  # Already YYYY-MM-DD
+    if len(time_str) >= 6 and time_str[:4].isdigit():
+        return time_str[:4] + '-' + time_str[4:6]  # YYYYMMDD → YYYY-MM
+    return time_str[:7]
+
+def _cached(key: str, fn, ttl: float = _CACHE_TTL):
+    """Return cached result or compute and cache it."""
+    now = time.monotonic()
+    if key in _cache:
+        ts, val = _cache[key]
+        if now - ts < ttl:
+            return val
+    val = fn()
+    _cache[key] = (now, val)
+    return val
+
+def get_db() -> Database:
+    """Get a Database instance using default config."""
+    config = Config.load()
+    return Database(config)