feat(02-03): Season-1 fragments + sim/memory selector + harvest/compost commands

Task 1 of Plan 02-03: ship Season-1 authored content + the deterministic
fragment selector + extend sim/garden/commands.ts with harvest + compost.

Content (≥17 Season-1 fragments under /content/seasons/01-soil/):
- 14 in fragments.yaml (9 warm / 3 contemplative / 2 heavy + 1 _meta sentinel)
- 2 long-form Markdown fragments (lura-first-letter.md, winter-rose-night.md)
- Pool depth (W6): warm pool ≥9 satisfies the worst-case all-rosemary
  playthrough at the 8th-harvest Lura threshold (CONTEXT D-14)
- All ids match /^season1\.[a-z0-9._-]+$/ (FragmentSchema regex; CLAUDE.md
  stable-string-ID rule); bible voice maintained throughout

FragmentSchema extension (back-compat — tags is optional):
- Optional `tags: z.array(z.string()).optional()` for tonal-register gating
- Reserved tag `_meta` excludes the exhaustion sentinel from the normal pool

src/sim/memory/ (new module):
- pool.ts — filterPool() pure helper (Season + tonal-register + no-dup gates)
- selector.ts — selectFragment() deterministic + mulberry32 PRNG +
  EXHAUSTION_FALLBACK_ID for Pitfall 8 fallback
- selector.test.ts — 16 tests covering gating / no-dup / determinism /
  sentinel-fallback / sentinel-exclusion-from-normal-pool
- index.ts — barrel; src/sim/index.ts re-exports

src/sim/garden/commands.ts (extended):
- harvest() pure command — empties tile, appends one fragment id,
  re-computes unlockedPlantTypes (Pitfall 10: thresholds checked AFTER
  the harvest commit). Refuses immature plants and OOR indices.
- compost() pure command — empties tile regardless of stage; no fragment
  yield (D-07); no resource refund (D-04 = infinite seeds).
- SimContext interface — application-layer-injected (fragments, currentSeason)
- simulateOneTick() takes optional ctx (default empty pool); harvest/compost
  branches added to the kind switch.
- BLOCKER 3 invariant preserved — sim writes tickCount, never lastTickAt.

Plant-type unlock thresholds (CONTEXT D-05, plan author's discretion):
- rosemary @ count 0 (start)
- yarrow @ count 3 (third harvest)
- winter-rose @ count 6 (sixth harvest)

commands.test.ts: +18 new cases (harvest / compost / Pitfall 10 boundary
on yarrow + winter-rose / sentinel fallback / immutability). 65/65 tests
green across src/sim/memory + src/sim/garden + src/content; lint exits 0;
build green (Vite parses all 17 fragments without schema violation).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

content/seasons/01-soil/fragments/lura-first-letter.md

@@ -0,0 +1,14 @@
+---
+id: season1.soil.lura-first-letter
+season: 1
+tags: [warm]
+---
+Lura wrote you a letter once, and never sent it. It was about a recipe — the
+proportions of vinegar to honey, and how long to let the onions sit. Most of
+the letter is the recipe. Two paragraphs at the bottom are about something
+else: a bee in a kitchen window, a song you didn't recognize, the shape your
+hand made on a glass.
+
+She left the letter in a drawer, decided it sounded too much. Then there was
+no drawer, and no letter. The recipe is real. You could find it again, if you
+asked.

content/seasons/01-soil/fragments/winter-rose-night.md

@@ -0,0 +1,13 @@
+---
+id: season1.soil.winter-rose-night
+season: 1
+tags: [heavy]
+---
+Winter-rose blooms at night. This is, technically, slander — the rose blooms
+when it blooms, and the night is when most people are asleep, and so the
+night is when most people fail to see things bloom. But the slander stuck.
+A flower for the people who couldn't sleep.
+
+Someone, in this place, used to set a chair by the window in February and
+wait. The wait was the thing. The flower would bloom in its own time. Most
+good things were like that, until they weren't.