PBI-58: Developer manual + in-app /manual page (#148)

* docs(PBI-58): add developer manual chapters under docs/manual/

Adds a 7-file English-language manual targeted at new human contributors:
index, overview, statuses & transitions (with mermaid state diagrams),
git workflow, MCP integration, docker, and troubleshooting. The manual
is the *map* — it cross-references existing runbooks/ADRs/architecture
docs rather than duplicating their content.

Regenerates docs/INDEX.md and validates with check-doc-links.mjs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* chore(PBI-58): add markdown rendering deps + manual:build script

Adds mermaid, rehype-slug, rehype-autolink-headings for the in-app
/manual page. Wires manual:build into prebuild so production builds
always regenerate the chapter TOC.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(PBI-58): codegen script for in-app manual TOC

scripts/build-manual.mjs walks docs/manual/, parses YAML front-matter,
strips it from the body, and emits lib/manual.generated.ts with a typed
ManualEntry[] containing slug, title, description, filePath, and the
embedded markdown body. Pure Node 20, mirrors generate-docs-index.mjs.

Inlining the markdown at build time keeps runtime serverless functions
free of filesystem reads, which avoids whole-project NFT tracing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(PBI-58): /manual route renders developer manual chapters in-app

Catch-all route at app/(app)/manual/[[...slug]]/page.tsx with
generateStaticParams covering every TOC entry. Server-side
MarkdownView uses react-markdown with remark-gfm, rehype-slug, and
rehype-autolink-headings; mermaid code blocks are routed to a
client-only MermaidBlock that dynamic-imports mermaid on mount.

ManualSidebar (client) reads the typed TOC and highlights the active
chapter via usePathname.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(PBI-58): add Manual link to main nav bar

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

components/shared/nav-bar.tsx

@@ -143,6 +143,7 @@ export function NavBar({
             : disabledSpan('Solo')}
           {navLink('/insights', 'Insights', pathname.startsWith('/insights'))}
           {navLink('/ideas', 'Ideas', pathname.startsWith('/ideas'))}
+          {navLink('/manual', 'Manual', pathname.startsWith('/manual'))}
           {roles.includes('ADMIN') && navLink('/admin', 'Admin', pathname.startsWith('/admin'))}
         </nav>
       </div>