docs: convert all architecture .adoc sections to markdown, prettier-format all .md

- Converted 13 individual .adoc section files to .md via
  asciidoctor→docbook5→pandoc(gfm) + post-processing, placed alongside
  the .adoc sources in Docs/Architecture/
- Rebuilt architecture.md from the individual section .md files
- Ran prettier --write on all .md in the repo (23 files changed):
  normalised table column alignment, trailing whitespace, line breaks
- Added .agents/ to .prettierignore (vendored third-party content)
- All .md now passes prettier --check

Docs/release-checks.md

@@ -35,12 +35,12 @@ Measured at 1440p on the development workstation: Bazzite, Ryzen 7 7700X, 64 GB
 
 ## Check-record template
 
-| Version | Check | Result | Evidence | Date |
-| --- | --- | --- | --- | --- |
-| `0.1.0` | Traversal, both sides | — | — | — |
-| `0.1.0` | Placement vs references | — | — | — |
-| `0.1.0` | Collision and packaging | — | — | — |
-| `0.1.0` | 60 FPS at 1440p | — | — | — |
-| `0.1.0` | Fresh checkout build | — | — | — |
-| `0.1.0` | Packaged Linux build | — | — | — |
-| `0.1.0` | Attribution display | — | — | — |
+| Version | Check                   | Result | Evidence | Date |
+| ------- | ----------------------- | ------ | -------- | ---- |
+| `0.1.0` | Traversal, both sides   | —      | —        | —    |
+| `0.1.0` | Placement vs references | —      | —        | —    |
+| `0.1.0` | Collision and packaging | —      | —        | —    |
+| `0.1.0` | 60 FPS at 1440p         | —      | —        | —    |
+| `0.1.0` | Fresh checkout build    | —      | —        | —    |
+| `0.1.0` | Packaged Linux build    | —      | —        | —    |
+| `0.1.0` | Attribution display     | —      | —        | —    |