Add per-hex metadata system for scale-invariant classification

Each hex now gets a meta/<q>_<r>.json with stable ID, pixel center
coordinates, pixel bounds, labels, notes, and classification status.
The pixelCenter acts as a scale-independent anchor: when switching from
10 Meilen/Hex to 5 Meilen/Hex, pixelToAxial(meta.pixelCenter, newSize)
maps coarse hexes to fine hexes without re-running classification.

Adds:
- pipeline/build-hexmeta.ts: creates/updates metadata + exports
  data/hexmeta-<map-id>.jsonl (committed, survives git clones)
- pipeline/auto-classify-ocean.ts: pixel-based ocean auto-detection
- pipeline/create-map.ts: one-off DB map entry creation
- extract-submaps.ts: writes meta/<q>_<r>.json during extraction
- data/hexmeta-1.jsonl: 8844 hex metadata entries for Aventurien map 1

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

package.json

@@ -14,6 +14,7 @@
     "pipeline:tiles": "tsx pipeline/generate-tiles.ts",
     "pipeline:assemble": "tsx pipeline/assemble-map.ts",
     "pipeline:extract":  "tsx pipeline/extract-submaps.ts",
+    "pipeline:hexmeta":  "tsx pipeline/build-hexmeta.ts",
     "pipeline:import":   "tsx pipeline/import-from-json.ts"
   },
   "devDependencies": {