feat(02-02): sim/garden — types, plants table, growth state machine, plantSeed

- src/sim/garden/types.ts: Tile/PlantInstance/PlantType/PlantTypeId/GrowthStage interfaces; tileIdx(row,col) + tileCoords(idx) + emptyTiles() helpers (RESEARCH Pitfall 2 canonical row*4+col encoding)
- src/sim/garden/plants.ts: 3 Season-1 plants per D-03 (rosemary 600t / yarrow 900t / winter-rose 1500t — D-08/D-09 2–5min band) with placeholder tints (D-26)
- src/sim/garden/growth.ts: advanceGrowth() pure function — Sprout (0%) → Mature (33%) → Ready (100%); Math.max clamp on negative deltas defends Pitfall 1 system-clock rewind
- src/sim/garden/commands.ts: plantSeed (D-05 unlock-gate + occupied silent no-op + immutability) + simulateOneTick (BLOCKER 3 — writes tickCount, NEVER lastTickAt) + tileGrowthStage helper
- src/sim/garden/index.ts: barrel
- src/sim/index.ts: re-export garden barrel
- 25 new tests (11 growth + 14 commands) — all green; lint clean; build green
- ESLint sim-purity rule from Plan 02-01 confirms zero Date.now/setInterval call sites under src/sim/garden/

src/sim/garden/index.ts

@@ -0,0 +1,9 @@
+/**
+ * Public barrel for src/sim/garden/. App code imports from here, never
+ * from the individual module files.
+ */
+export type { Tile, PlantInstance, PlantType, PlantTypeId, GrowthStage } from './types';
+export { GRID_ROWS, GRID_COLS, GRID_SIZE, tileIdx, tileCoords, emptyTiles } from './types';
+export { PLANT_TYPES, getPlantType } from './plants';
+export { advanceGrowth, GROWTH_THRESHOLDS } from './growth';
+export { plantSeed, simulateOneTick, tileGrowthStage } from './commands';