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/templates/timeline.html

@@ -141,9 +141,12 @@ if (points.length > 0 && months.length > 0) {
         };
     });
 
-    // --- Initial plot (first month) ---
-    const firstTraces = buildTraces(months[0]);
-    const firstCount = points.filter(p => p.month <= months[0]).length;
+    // --- Initial plot: show the FULL landscape (last frame) so the page
+    //     doesn't open on the near-empty earliest month. Play replays from
+    //     the start to animate the build-up. ---
+    const initMonth = months[months.length - 1];
+    const initTraces = buildTraces(initMonth);
+    const initCount = points.length;
 
     // Slider steps
     const sliderSteps = months.map(month => ({
@@ -165,7 +168,7 @@ if (points.length > 0 && months.length > 0) {
                 {
                     label: '&#9654; Play',
                     method: 'animate',
-                    args: [null, { frame: { duration: 500, redraw: true }, transition: { duration: 300 }, fromcurrent: true }]
+                    args: [null, { frame: { duration: 500, redraw: true }, transition: { duration: 300 }, fromcurrent: false }]
                 },
                 {
                     label: '&#9724; Pause',
@@ -175,7 +178,7 @@ if (points.length > 0 && months.length > 0) {
             ]
         }],
         sliders: [{
-            active: 0,
+            active: months.length - 1,
             steps: sliderSteps,
             x: 0.05, len: 0.9,
             xanchor: 'left',
@@ -194,13 +197,13 @@ if (points.length > 0 && months.length > 0) {
         }],
     };
 
-    Plotly.newPlot('tsneAnim', firstTraces, layout, CFG).then(() => {
+    Plotly.newPlot('tsneAnim', initTraces, layout, CFG).then(() => {
         Plotly.addFrames('tsneAnim', frames);
     });
 
     // Update badge on animation frame
     const badge = document.querySelector('#monthBadge span');
-    badge.textContent = `${fmtMonth(months[0])} — ${firstCount} drafts`;
+    badge.textContent = `${fmtMonth(initMonth)} — ${initCount} drafts`;
 
     document.getElementById('tsneAnim').on('plotly_animatingframe', function(ev) {
         const month = ev.name;