feat(02-02): begin screen + seed picker + ui-strings + lazy content split

- content/seasons/01-soil/ui-strings.yaml: player-visible Phase-2 copy externalized per CLAUDE.md (Begin / seed picker / post-harvest beat / journal / settings / plant display names); voice reviewed against bible + anti-fomo-doctrine.md
- content/seasons/01-soil/fragments.yaml: placeholder Season-1 fragment file (Plan 02-03 expands to ≥10 authored)
- content/seasons/00-demo/: deleted (Phase-1 demo replaced)
- src/content/schemas/ui-strings.ts: UiStringsSchema (Zod) — validates structure of every season's ui-strings.yaml at load time
- src/content/schemas/index.ts + src/content/index.ts: re-export UiStringsSchema/UiStrings
- src/content/loader.ts: eager `uiStrings` glob + PIPE-02 lazy `loadSeasonFragments(seasonId)` (Plan 02-03+ exploit)
- src/ui/begin/use-audio-bootstrap.ts: bootstrapAudioContext() lazy-creates + resumes (RESEARCH Pattern 9; Pitfall 5 mitigation — context construction inside the gesture for iOS Safari) + installFirstInteractionGestureHandler() one-shot for D-22 returning players + __resetAudioBootstrapForTest()
- src/ui/begin/BeginScreen.tsx: D-21 typographic Begin screen — title + subtitle + CTA from uiStrings[1].begin; onClick calls bootstrapAudioContext synchronously inside the click event then dismisses the session gate (D-22)
- src/ui/begin/BeginScreen.test.tsx: 4 tests — render / D-22 skip / click bootstraps + dismisses / subtitle string
- src/ui/garden/SeedPicker.tsx: D-02 inline DOM popover; subscribes to 'tile-clicked-coords'; renders one button per unlocked plant type from uiStrings[1].plants; click enqueues plantSeed command via store.enqueueCommand
- src/ui/garden/SeedPicker.test.tsx: 6 tests — initial-null / coords-positioned / unlocked-only / enqueue / dismiss / multi-plant; mocks game/event-bus to avoid Phaser canvas init under happy-dom (deviation Rule 3)
- src/ui/{begin,garden,index}.ts: barrels
- src/App.tsx: mount BeginScreen + SeedPicker as overlay siblings to PhaserGame
- src/PhaserGame.tsx: bootstrap unlockedPlantTypes=['rosemary'] for first-run; install gesture handler + scene-ready listener
- npm run ci exits 0; 163/163 tests pass (10 new this commit + 25 from Task 1 + 128 baseline)

content/seasons/01-soil/fragments.yaml

@@ -0,0 +1,10 @@
+# /content/seasons/01-soil/fragments.yaml
+#
+# Phase 2 placeholder. Plan 02-03 replaces with the authored Season-1
+# fragments (≥10 in voice, MEMR-* coverage). The single placeholder
+# fragment here keeps the eager fragment loader green during Plan 02-02
+# (Plan 02-03 expands the file).
+fragments:
+  - id: season1.soil.placeholder
+    season: 1
+    body: "(placeholder — Plan 02-03 ships authored fragments)"