docs: v0.1.0 alpha framing + hygiene pass (#25)

Update the public-facing docs to the M-49 state (v0.1.0 alpha, first
full-campaign playtest: 19/21 missions completable, D191 crashes Bunker ii
+ Statue, D193 AI pacing is the top flaw).

- README: lead with what it is + status, research angle second; new
  Quick start section; Status/Download rewritten for the alpha + dual
  platform; "By the numbers" refreshed (~3 weeks, ~320 commits, ~190
  findings, ~49 sessions, 69 PORT files).
- .github/release-notes.md: v0.1.0 title + known-issues rewrite.
- .github/social-preview.html: status/stat lines (regen + re-upload the
  PNG separately).
- docs/index.md, docs/dev/LEVEL-STATUS.md: M-49 status.
- docs/dev/findings.md, docs/dev/GRAPHICS-BACKLOG.md: D191-D197 +
  D148/D170/D173 M-49 escalations.

Hygiene:
- Fix the `&` literal in internals.md H1.
- Repoint two ../README.md links that 404 on the Pages site.
- Standardise British -> American spelling across the public docs
  (behaviour->behavior, colour->color, catalogue->catalog,
  centre->center, etc.). Deep internal logs left untouched.
- .gitignore: document the local-notes convention (docs/HANDOFF.md,
  docs/BACKLOG.md, and a new docs/dev/notes/ drop for roadmaps and
  session plans) so it survives a fresh clone.

docs/index.md

@@ -17,8 +17,10 @@ unfamiliar, low-level codebase**: two coding agents — a local open-weight mode
 part-time through ~230 translation units of unmodified big-endian MIPS game
 code, handing work back and forth through shared written notes.
 
-**Status:** Phase 2 of 4 (rendering). Boots, renders the full intro and front
-end, loads all 21 solo missions. No audio yet; not playable end to end.
+**Status:** Phase 2 of 4 (rendering); first alpha **v0.1.0** released. Runs the
+full single-player campaign — 19 of 21 missions completable start to finish in
+a full-campaign playtest, two levels still crash mid-mission. No audio yet; AI pacing
+and cutscenes are rough.
 
 - **[Project repository and README](https://github.com/jkdansereau/goldeneye-pc-port)** — build instructions, requirements, status, how it compares to the Xbox 360 recompilation projects.
 
@@ -28,5 +30,5 @@ end, loads all 21 solo missions. No audio yet; not playable end to end.
 - **[Development process](dev-process.md)** — how work was scoped, partitioned, and budgeted across agents; the finding-log discipline.
 - **[Internals](internals.md)** — architecture, the software RSP-emulation approach, GoldenEye-vs-Perfect-Dark engine differences, the phased plan.
 - **[Porting notes](porting-notes.md)** — the recurring Nintendo 64 → PC bug classes hit during the port, with fixes.
-- **[Game-behaviour reference](dev/game-behavior-reference.md)** — how the retail N64 game is meant to behave: combat/AI model, difficulty scaling, per-level objectives, timers, weapon data, and the original game's known quirks.
+- **[Game-behavior reference](dev/game-behavior-reference.md)** — how the retail N64 game is meant to behave: combat/AI model, difficulty scaling, per-level objectives, timers, weapon data, and the original game's known quirks.
 - **[Building](building.md)** — full build and asset-extraction guide.