docs(site): fix landing-page facts, document shipped features, refresh changelog/roadmap

[Papyszoo]

Summary

Fixes every issue found in the docs-site review: factual errors on the landing page, wrong facts in user docs, and shipped features that had zero documentation.

Landing page (docs/src/pages/index.tsx)

• Fixed the broken quick start: step 2 pointed at http://localhost:3000 — corrected to https://localhost:3010; step 1 now includes cp .env.example .env and offers the desktop installers first (they were absent from the page entirely)
• Removed the "Blender Addon" card (no addon exists) — replaced with the real WebDAV + Blender workflow (save a .blend into the mounted drive → new model version)
• Honest licensing wording: "Open Source" badge/stat/CTA → "Source Available" / "Self-Hosted & Local-First" (BSL 1.1 is source-available, not OSI open source)
• Multi-asset pitch: hero retitled "Your Personal Game Asset Library", subtitle and feature cards now cover textures, sprites, sounds, env maps, and scripts — not only 3D models
• Live Demo is now a primary hero CTA instead of a navbar-only link
• Config tagline updated to "Self-hosted game asset library"

User docs — factual fixes

• texture-sets.md tagging section claimed one shared tag vocabulary across asset types — corrected to per-asset-type vocabularies (matches 0.3.0 behavior)
• models.md formats: added STL and 3MF
• sounds.md formats: added AAC and M4A; sprites.md widened to the actual accepted image formats

User docs — previously undocumented features

• New scripts.md page: upload/create flows, supported languages, CodeMirror editor, live GLSL/HLSL preview on primitives or your own models, built-in + custom templates, category tree, packs/projects/recycle integration
• user-interface.md: tab table now covers all tab types (Global Materials, Multi-Model Textures, Scripts, History, viewers), plus new sections for the New Tab page (tiles, Recently Closed, Sessions) and Global Search (Ctrl/⌘ + K)
• texture-sets.md: new "Texture Set Kinds" section (Global Materials vs Multi-Model Textures)
• Scripts added to packs/projects/recycled-files/intro pages; sidebar renumbered accordingly
• Stages intentionally not documented — the tile is disabled ("under rework"); the roadmap explains why

Changelog & roadmap

• changelog.md now leads with per-release highlights (0.1.0 → 0.3.1) and points to GitHub Releases as the canonical changelog; old entries preserved as pre-release development notes (it previously ended at 2026-04-10, before any release)
• roadmap.md rewritten from an internal AI-agent task list into a human-readable direction page (ingest → animations/rigs → export → data safety → distribution, with explicit out-of-scope items)

Cleanup

• ci-cd-pipeline.md moved under a collapsed Development sidebar category
• Deleted default Docusaurus leftovers: markdown-page.md, unused HomepageFeatures component, undraw_* images, docusaurus.png

Verification

npm run build in docs/ passes (onBrokenLinks: "throw" — no broken links, client + server bundles compile).

Feature claims were verified against the frontend source (tab types in shared/types/ui.ts, New Tab tile catalog, script viewer menubar geometries, upload accept lists) rather than copied from old docs.

[Papyszoo]

Added docs:audit to this PR (it enforces exactly what this PR fixes): a zero-dependency CI check (npm run docs:audit, Docs Audit job on every push/PR) that fails when docs contradict code — format lists vs the FileType registry, user-interface.md tab coverage vs the TabType union, quick-start URLs vs FRONTEND_PORT, video embeds vs the video manifest. The README format check is a warning until #557 merges (flip noted in the script). Verified green here and red against injected drift (removed STL/3MF from models.md, reverted port to 3000 — both caught).