fix(webui): timeline opens on full landscape, drop undated points

After the chronological-order fix the page opened on the earliest month
(1995-12), showing only a handful of same-colored dots while the legend
listed every category — looked broken.

- Initialise the plot on the LAST frame (full landscape); Play now replays
  the build-up from the start (fromcurrent: false), slider starts at the end.
- Make _extract_month robust: year-only / junk dates (ISO/ETSI 'time' like
  '2015/CD Amd 2', bare '2023', '') no longer yield malformed month labels
  ('2015-/C') or a garbled 'unknown' frame badge.
- Drop undated docs from the temporal animation (they remain on /landscape).

At the full initial frame every category has points, so the legend matches
what is drawn.

src/webui/data/_shared.py

@@ -20,14 +20,17 @@ _CACHE_TTL = 300  # 5 minutes
 
 
 def _extract_month(time_str: str | None) -> str:
-    """Normalize a date string to YYYY-MM format."""
+    """Normalize a date string to YYYY-MM (or "unknown" if unparseable)."""
     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]
+    s = time_str.strip()
+    if len(s) >= 7 and s[4] == '-' and s[5:7].isdigit():
+        return s[:7]  # ISO 8601: YYYY-MM-DD...
+    if len(s) >= 6 and s[:6].isdigit():
+        return s[:4] + '-' + s[4:6]  # Compact: YYYYMMDD → YYYY-MM
+    if len(s) >= 4 and s[:4].isdigit():
+        return s[:4] + '-01'  # Year-only / year-prefixed junk (e.g. "2015/CD Amd 2")
+    return "unknown"
 
 def _cached(key: str, fn, ttl: float = _CACHE_TTL):
     """Return cached result or compute and cache it."""

src/webui/data/analysis.py

@@ -546,6 +546,8 @@ def _compute_timeline_animation_data(db: Database) -> dict:
         r = rating_map[name]
         d = draft_map.get(name)
         month = _extract_month(d.time if d else None)
+        if month == "unknown":
+            continue  # Undated docs (e.g. ISO/ETSI) can't be placed on a temporal animation
         cat = r.categories[0] if r.categories else "Other"
         month_set.add(month)
         category_monthly[month][cat] += 1