docs: SEO round 2 (Bing) - demote per-page h1 to h2 site-wide, re-trim meta description, bump README/Pages to v0.2.1

Bing Webmaster re-flagged the site after the first SEO pass (32f193a0):
- Every Jekyll-processed doc page (building.md, dev-process.md, internals.md,
  porting-notes.md, dev/agentic-development.md, plus index.md caught last
  time) opens with its own "# Heading" on top of the Cayman theme's masthead
  <h1 class="project-name">, so all of them emitted two h1 tags, not just the
  homepage. Demoted each page's opening heading to h2 -- anchor slugs are
  unaffected (kramdown ids don't depend on heading level).
- index.md's meta description was 161 chars (1 over Bing's 160 limit) and
  still said v0.2.0; re-trimmed to 133 chars and bumped to v0.2.1.
- README.md and docs/index.md's Status lines/comparison table bumped from
  v0.2.0 to v0.2.1 to match the actual current release.

Verified against a live, cache-busted fetch of the deployed Pages site
(the first Bing report was reading a stale CDN edge cache from before the
32f193a0 deploy, per its own Last-Modified header) that the underlying fix
was already live; this pass addresses what was still genuinely wrong.

Claude-Session: https://claude.ai/code/session_01KwZViAFaXua3PKgHHjNgvi

docs/index.md

@@ -1,10 +1,10 @@
 ---
 title: GoldenEye 007 PC Port
-# v0.2.1 (Bing SEO): meta description trimmed to ~160 chars (was 277).
+# v0.2.1 (Bing SEO round 2): re-shortened to 133 chars (was 161, 1 over
+# Bing's 160 limit) and bumped the stale v0.2.0 mention.
 description: >-
   A native PC port of the 1997 N64 classic, built from decompiled source with
-  a software RSP. v0.2.0 for Windows and Linux (incl. Steam Deck) -- bring
-  your own ROM.
+  a software RSP. v0.2.1 for Windows, Linux and Steam Deck.
 ---
 
 <!-- v0.2.1 (Bing SEO): the "# GoldenEye 007 PC Port" h1 was removed here --
@@ -17,7 +17,7 @@ N64's graphics coprocessor (RSP) running in software, the same architecture
 as the [Perfect Dark PC port](https://github.com/fgsfdsfgs/perfect_dark), the
 same Rare "Indy" engine family, one hardware generation apart.
 
-**Status: v0.2.0.** The full single-player campaign runs at a steady 60 fps
+**Status: v0.2.1.** The full single-player campaign runs at a steady 60 fps
 and is completable end to end; all 21 missions load and run clean on Windows
 and Linux (one intermittent Steam Deck crash remains, listed below), and
 audio (music + SFX) plays throughout. The known