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/01_introduction_and_goals.md

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+# Introduction and Goals
+
+Gig Line is a Linux-first Unreal Engine 5 game that reconstructs a walkable (and eventually drivable) stretch of Hollywood Boulevard around 6840 Hollywood Blvd / El Capitan Entertainment Centre. The initial release (`0.1.0`) delivers a first-person walking demo of the south-side block between Highland Avenue and Orange Drive, plus north-side buildings within 50 m of the frontage.
+
+## Requirements Overview
+
+| ID | Description |
+| --- | --- |
+| F-1 | Walk both sides of Hollywood Blvd in the demo area without falling through geometry |
+| F-2 | First-person movement (WASD + mouse look), jump, reset (R), pause (Escape) |
+| F-3 | Fixed daytime lighting and atmosphere (sun, sky, fog, exposure) |
+| F-4 | Geographic attribution display (ODbL: "© OpenStreetMap contributors" + licence link) |
+| F-5 | Designated street crossing with zebra markings at signalised crossings |
+| F-6 | Building façades recognisable against reference photography |
+| F-7 | Terrain, road, and sidewalk follow real-world DEM elevation |
+| F-8 | 60 FPS at 1440p on the documented workstation and quality preset |
+
+Full requirements and progress are in [TODO.md](../../TODO.md); version direction is in [ROADMAP.md](../../ROADMAP.md).
+
+## Quality Goals
+
+| Priority | Quality Goal | Scenario |
+| --- | --- | --- |
+| 1 | **Performance efficiency** | 60 FPS at 2560×1440 on RTX 5070 Ti, documented preset, no frame generation |
+| 2 | **Terrain walkability** | Zero raycast holes across both sidewalks and the carriageway (84-sample transect passes) |
+| 3 | **Geographic fidelity** | Building placement, street scale, and façade identity match reference photography |
+| 4 | **Build reproducibility** | Fresh checkout + documented engine path produces a runnable Linux build |
+| 5 | **Licensing compliance** | Every redistributable asset has verified provenance; ODbL attribution is visible at runtime |
+
+## Stakeholders
+
+| Role | Contact | Expectations |
+| --- | --- | --- |
+| Owner / Director | zwitschi | Sets scope, approves screenshots, cuts release tags |
+| AI coding agents | multiple sessions | Read `AGENTS.md`, `TODO.md`, `ROADMAP.md`, and this document for architecture constraints; never commit directly to `main` |
+| Players | end users | Walk the demo at 60 FPS without falling through the world; see a recognisable Hollywood block |
+| OSM contributors | OpenStreetMap | ODbL attribution is displayed and derivative-database obligations are met |