docs: review follow-ups (about render fix, audience intros, api-contracts routes, install-guide cleanup)

Documentation follow-ups from the consistency review (the CRITICAL/MAJOR accuracy fixes landed in !221 (merged); the gpu value over-correction was reverted in !222 (merged)).

This MR

• /about/ rendering fix — root cause: Docsy's navbar is position:fixed, and the about page uses the default layout (<main class=td-main>) which Docsy only offsets via .td-main main (a descendant that doesn't match the <main class=td-main> element) → content hid under the navbar. Fixed via site/assets/scss/_styles_project.scss (padding-top on .td-main + scroll-margin-top on headings). Also restored the visible H1 (td-default doesn't render the front-matter title as h1).
• Audience-framing intros added to the 3 pages missing them (state-management, theme-system, mobile-architecture).
• source-tree-analysis: vite.config.js → vue.config.js (frontend uses Vue CLI — no vite.config.js exists).
• api-contracts-backend: added the missing /admin/queries/inspect + /:queryId admin routes (Query Inspector).
• install-guide: removed 19 stray Confluence label lines (bare Bash/Plaintext rendered as literal text), fixed escaped list markers, fixed the inconsistent clone URL (fordendk/genie-ai-replica → real remote).
• integration-architecture: ARANGO_USER snippet hardcoded 'root' → process.env.ARANGO_USER || 'root'; removed the leaked "Document History" scan artefact.

Build verified clean.

Deliberately deferred (judgment-heavy, risk of over-trimming)

• Cross-page layer-stack drawn 3× (project-overview / integration-architecture / architecture) — the overview's brief stack is appropriate for orientation; deep dedup risks removing integration-specific content. Leaving as-is unless you want a specific trim.
• Keycloak admin-user + self-signed-cert decision matrix duplicated across compose/swarm/install — would consolidate into one owned page; non-trivial restructure.