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/Architecture/11_technical_risks.md

@@ -0,0 +1,11 @@
+# Risks and Technical Debts
+
+| ID | Risk / Debt | Priority | Mitigation |
+| --- | --- | --- | --- |
+| R-1 | Terrain bbox proxy misdiagnosed as fall-through — already fixed, but the root-cause path (Interchange defaults to simple collision) could recur on reimport | High | `UGigLineAssetTools` runs in the build script; always reassert complex-as-simple after any reimport. Documented in `MEMORY.md` and ADR-3. |
+| R-2 | Blosm 3Dsimple on Blender 5.2 — worked around, not resolved; `3Drealistic` mode untested | Medium | Pin Blosm 2.7.28 and Blender 5.2 LTS; test realistic mode before depending on it. |
+| R-3 | Kerb height is an assumption (DEM does not resolve it) | Medium | Record the assumption in `Geo/verification/`; measure from reference photography if possible; mark as unresolved until verified. |
+| R-4 | ODbL derivative-database posture for shipped builds is open | Medium | In-game attribution is done; legal review of shipped-DB obligations needed before public release. |
+| R-5 | `GigLine SIM` / `GigLine GROUND` TEMP diagnostic logging still in `GigLineCharacter.cpp` | Medium | Strip behind a cvar or remove entirely before the `v0.1.0` release tag. |
+| TD-1 | Materials are Unreal-only — no Blender preview round-trip | Low | Accepted (ADR-2). Look-dev happens in UE; screenshot review catches issues. |
+| TD-2 | No CI pipeline — all builds and QA are manual on the dev workstation | Low | Acceptable for `0.x`. CI is a `0.3.0+` concern. |