P20: map viewport zoom/pan/fit + token placement palette

Render maps at natural resolution inside a CSS-transform world layer (zoom,
pan, fit-to-view) instead of shrinking to maxWidth — large maps are now usable.
Pure viewport math in src/lib/map/viewport.ts (unit-tested). New TokenPalette
places party PCs / active-encounter combatants / blanks in one click with dup
detection; tokens gain optional combatantId (Dexie v9) for live encounter HP.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/db/db.ts

@@ -96,6 +96,10 @@ export class TtrpgDatabase extends Dexie {
           }
         });
     });
+
+    // v9 — Phase 20: tokens gain optional combatantId (live HP from an encounter
+    // combatant). Optional field — no backfill needed; existing rows parse fine.
+    this.version(9).stores({});
   }
 }