Bug fix
- electron/main.ts: the static-export server's path-traversal guard rejected
  any request whose path contained "..", which 403'd Turbopack's content-
  hashed CSS chunks (e.g. `16-.0wq_hn57..css`) and rendered the entire
  packaged app unstyled. Replace the substring check with a per-segment
  check that only rejects true traversal segments ("..", ".").

Docs
- New ARCHITECTURE.md (326 lines): system diagram, renderer/backend layout,
  HTTP API contract, project layout, build-from-source, VM testing harness,
  pre-commit checks, contributing guide, release process.
- README.md rewrite: social-card hero, CI/release/downloads/license badges,
  "Why ProtonShift?" framing, consolidated Install section with copy-pastable
  per-format commands, ARCHITECTURE.md link in the nav strip, roadmap.

Version bump 0.9.6 -> 0.9.7 in all sources
- electron/package.json
- electron/renderer/package.json
- src/game_setup_hub/__init__.py
- assets/io.github.protonshift.metainfo.xml (new <release> entry, 2026-05-14)
- .github/ISSUE_TEMPLATE/bug_report.yml placeholder
- electron/renderer/src/components/nav-bar.tsx fallback string

Verification
- tsc on electron main: clean.
- next build (static export, Next 16.2.6): clean, 8/8 routes prerendered.
- 0 open Dependabot alerts on this branch (all 18 closed by v0.9.6).

Co-authored-by: Cursor <cursoragent@cursor.com>