Add a footer and an in-app docs viewer

Footer (in the authenticated app layout, matching where Nav lives):
copyright line, a Docs link, and a link to the project repo.

Docs viewer: /docs lists docs/API.md, CONFIG_REFERENCE.md, and
ARCHITECTURE.md; /docs/[slug] renders one via react-markdown +
remark-gfm (tables, fenced code) inside a Tailwind Typography `prose`
block, dark-mode aware via prose-invert. The markdown files themselves
stay the single source of truth at the repo's docs/ - the app reads
them at request time rather than duplicating their content, resolved
from the app's cwd the same way config paths already are, since a
compiled Route Handler's module graph doesn't preserve source-relative
paths.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/package.json

@@ -38,6 +38,8 @@
     "react": "19.2.8",
     "react-dom": "19.2.8",
     "react-hook-form": "^7.85.0",
+    "react-markdown": "^10.1.0",
+    "remark-gfm": "^4.0.1",
     "shadcn": "^4.18.0",
     "sonner": "^2.0.8",
     "tailwind-merge": "^3.6.0",
@@ -48,6 +50,7 @@
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",
+    "@tailwindcss/typography": "^0.5.20",
     "@types/better-sqlite3": "^9.6.0",
     "@types/node": "^20",
     "@types/react": "^19",