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

Geo/verification/2026-11-06-cross-sections.md

@@ -16,7 +16,7 @@ Those gutter positions bracket a carriageway of roughly **20–22 m**, which ind
 ## Section table
 
 | Along block | Lowest point | Road crown | Cross-fall across the road | Gutter candidates |
-| ---: | ---: | ---: | ---: | --- |
+| --: | --: | --: | --: | --- |
 | 0.0 m | 118.78 @ −10 | ~119.41 @ 0 | ~0.6 m / 2 % | −10, +10 |
 | 40.0 m | 118.43 @ −11 | ~118.94 @ 0 | ~0.5 m / 2 % | −11, +10.5 |
 | 80.0 m | 117.84 @ −10 | ~118.33 @ 0 | ~0.5 m / 2 % | −10, +10.5–11.5 |