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/internals.md

@@ -1,15 +1,16 @@
-# GoldenEye 007 — PC Port: architecture & plan
+# GoldenEye 007 — PC Port: architecture & plan
 
 > This began as the pre-implementation research note and is kept as the
 > architecture reference. Sections 1–9 describe the design; section 10 lists
 > external references. The phased plan in section 8 is largely done through
-> Phase 2 — for current status see the [README](../README.md) and
+> Phase 2 — for current status see the
+> [README](https://github.com/jkdansereau/goldeneye-pc-port#status) and
 > [`dev/LEVEL-STATUS.md`](dev/LEVEL-STATUS.md); for the blow-by-blow finding
 > log see [`dev/findings.md`](dev/findings.md).
 
 This document captures the research done to plan a PC port of
 GoldenEye 007, based on the decompilation this repository is forked from
-([`n64decomp/007`](https://github.com/n64decomp/007)). It is modelled on the
+([`n64decomp/007`](https://github.com/n64decomp/007)). It is modeled on the
 approach used by the
 [Perfect Dark PC port](https://github.com/fgsfdsfgs/perfect_dark),
 which ports the same Rare "Indy" engine (a later revision) to modern