chore: track the design docs in git (.gitignore !*.md)

AUDIT P1: every markdown design doc except CODEMAP.md was untracked, so
ARCHITECTURE / AUDIT / OPSTACK-PLAN / fable-idea / REVIEW_FINDINGS lived
only on disk. Replaces the single !CODEMAP.md exception with !*.md.

Also makes OPSTACK-PROGRESS.md commits actually record something, which
the unattended crash-safety discipline depends on.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,43 @@
+# CLAUDE.md — VoxelForge
+
+UE5 **density-field voxel terrain** plugin (strates / Marching Cubes / async streaming).
+Don't re-read the whole plugin — use the map.
+
+## ⛔ #1 rule: NEVER build or compile
+Jahni runs every build himself (he has the editor open; running it via Claude just burns cost).
+When code changes are done, **stop and say "ready to build"** + list likely compile-error spots,
+then wait for his results / pasted errors. Same for in-editor checks — ask for a screenshot, don't
+try to run anything.
+
+## Read first (in order, load only what the task needs)
+- **[CODEMAP.md](CODEMAP.md) — ALWAYS.** Navigation: what it is, data-flow (§2), symbol→`file:line`
+  index (§3), "I want to change X → go here" (§5), conventions & gotchas (§6). Trust **symbol names
+  over line numbers** (lines drift).
+- **[ARCHITECTURE.md](ARCHITECTURE.md) — when touching generation / strates / passages / biomes.**
+  The deep design (archetypes, (0,0) spine, disturbances, content/atmosphere, biomes) **and the
+  `§8.10` performance invariants ("don't regress").**
+- **[fable-idea.md](fable-idea.md) — before planning PERF or FEATURE work.** Ranked perf+feature
+  roadmap with verified hot spots; check it so you don't re-propose done/known work. (A perf pass
+  already shipped: game thread solved ~3.94 ms, CullTiles spiral fixed, region-granular foliage.)
+- **[REVIEW_FINDINGS.md](REVIEW_FINDINGS.md)** — open quality/cleanup items (cross-check vs fable-idea
+  before acting; some may already be addressed).
+
+## Hard rules (these prevent real bugs — verify against code, don't assume)
+- **Density sign: negative = solid, positive = air** (MC convention at the mesher).
+  `FVoxelModification::Strength` negative = carve. *The #1 source of confusion.*
+- **Density functions take VOXEL coords, not cm.** Conversions live in `VoxelTypes.h`.
+- **Determinism:** all randomness = hash of (coord, seed, strateIndex). No RNG state — same seed ⇒
+  same world. Player edits (diff layer) are the only non-deterministic overlay.
+- **Async safety:** worker tasks only READ Generator/Mesher, must check `bShuttingDown`, and return via
+  `ProcessQueue` (must stay `EQueueMode::Mpsc`). `EndPlay` blocks on `ActiveTaskCount → 0`.
+- **Carry the `Epoch`** through any new async path (stale results are dropped on mismatch).
+- **Don't "optimize" the perf invariants** in ARCHITECTURE `§8.10` — the `thread_local` box-valid
+  caches, two-pass MC loop, SSE noise, and clipmap streaming are intentional.
+- **Never edit** `Binaries/`, `Intermediate/`, `*.generated.h`. Comments are French + English — match
+  the surrounding file.
+
+## Discipline (keep the map alive)
+- Add / rename / move a symbol → update its **CODEMAP §3** row (symbol-first; line is a hint).
+- Change generation/strate design → update **ARCHITECTURE §8**.
+- Resolve a checklist item → tick it in **REVIEW_FINDINGS.md**.
+- Don't duplicate content across these files — each has one job (map / design / findings / rules).