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)

src/content/schemas/ui-strings.ts

@@ -0,0 +1,37 @@
+import { z } from 'zod';
+
+/**
+ * Player-visible UI strings, externalized per CLAUDE.md "Code Style":
+ *   "Player-visible strings are externalized in /content/, never hardcoded."
+ *
+ * One file per season under /content/seasons/<slug>/ui-strings.yaml. The
+ * loader (src/content/loader.ts) keys them by `season` so the runtime can
+ * resolve `uiStrings[1].begin.title` etc.
+ */
+export const UiStringsSchema = z.object({
+  season: z.number().int().min(0).max(7),
+  begin: z.object({
+    title: z.string().min(1),
+    subtitle: z.string().min(1),
+    cta: z.string().min(1),
+  }),
+  seed_picker: z.object({
+    title: z.string().min(1),
+    cancel: z.string().min(1),
+  }),
+  post_harvest_beat: z.array(z.string().min(1)).min(1),
+  journal: z.object({
+    empty_state: z.string().min(1),
+    back: z.string().min(1),
+  }),
+  settings: z.object({
+    title: z.string().min(1),
+    export: z.string().min(1),
+    import: z.string().min(1),
+    restore_snapshot: z.string().min(1),
+    persistence_denied_toast: z.string().min(1),
+  }),
+  plants: z.record(z.string(), z.string().min(1)),
+});
+
+export type UiStrings = z.infer<typeof UiStringsSchema>;