fix(street-level): Panoramax IC8 round 2 — shared point budget, selected line, cone cache, DP segments

From the round-2 verification (approve with follow-ups), all follow-ups:
- The point budget is shared across the tiles in view once loading
  settles (water-filling): a sparse tile keeps what it has, a dense city
  centre takes the rest instead of drawing thinner than its suburbs. The
  selected sequence is always drawn, and selecting one a cap had left out
  draws it.
- The cones' picture-list cache keeps only finished lists: a re-centre
  while the cones loaded inherited the aborted load's tiles and drew
  none in them.
- Douglas–Peucker measures to the segment, so dead ends and U-turns keep
  their far end.
- Switching Panoramax off lets its decoded tiles and lists go.
- Picture downloads are counted while they stream (a host sending no
  length cannot fill memory before the cap).
- Comments on the via caption and the simplification tolerance match the
  code.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/CURRENT-STATE.md

@@ -3256,7 +3256,16 @@ IGN, MapComplete…; IGN's redirect to its OVH object storage). Its chip
 vector tiles (`/api/map/{z}/{x}/{y}.mvt`, an hour's HTTP cache): sequence
 lines from z14 below 1.8 km above ground, z13 to 5 km, z12 to 12 km, z11
 to 30 km and z10 to 60 km, as Mapillary's (a dense z10 tile over Paris is
-~2.1 MB and 8,600 sequences; each tile draws its 1,600 longest), and above
+~2.1 MB and 8,600 sequences, 750,000 points). `decode.js` simplifies each
+line (Douglas–Peucker to the segment, 4 units of a 4,096 tile: about a
+pixel where it is drawn, 6–10% of a GPS track's points), and the tiles in
+view draw their longest lines within 90,000 points (`maxPoints`,
+`keepOrder`), shared out once loading settles so a sparse tile keeps all
+it has and a dense one (a city centre) takes the rest; the selected
+sequence is always drawn. Every point becomes ~8 ground-line vertices:
+unsimplified, the lines hung the tab. Decoded tiles are kept while the
+provider is on (16, ten minutes, `tileCache.js`, shared with KartaView),
+and above
 60 km the `grid` layer's 0.1°
 density cells, binned to at most 96×96 points a tile (a z0 tile holds
 ~70,000 cells) and not counted as sequences: the panel says to zoom in. Both