feat: homepage onboarding flow and AI-native software templates

[johnnyhuy]

Closes#87
Closes#88

#87 — Homepage onboarding flow

Reorients the homepage around first-use orientation without removing catalog surfaces:

• Start here panel (directly under the hero): three concrete first actions — create your first service (/self-service), browse the docs (/docs), register an existing repo (/catalog-import). Replaces both the one-line Getting Started? alert and the near-identical Quick Actions grid (consolidated rather than duplicated; API Explorer moved to the sidebar).
• Onboarding Docs section: surfaces up to 4 catalog entities tagged onboarding or getting-started as cards linking to their TechDocs pages. Skeleton loaders while loading, graceful empty state explaining the onboarding tag when none exist.
• Support & Reference sidebar panel: replaces Quick Links with Documentation, API Reference, Notifications, and Get Help. The Get Help link is entity-driven — it points at the docs of a support-tagged entity when one exists, falling back to /docs.
• Removed the duplicate Getting Started sidebar card (per PRD note).
• All new links carry descriptive aria-labels; cards stack vertically at ≤600px via the existing Grid breakpoints; no hard-coded hex, all colours via theme.palette.*.
• New portal-docs TechDocs entity (examples/portal-docs/) with Getting Started and Support & FAQ pages, tagged onboarding / getting-started / support, so the new sections have real content on first boot.

#88 — Reusable software templates

• Family/provider tagging on all existing templates: family:repo, family:docs, provider:github, provider:gitlab; the two docs-site templates now carry recommended too.
• Homepage Popular Templates now filters to recommended-tagged templates and renders a family chip on each card; the action button reads "See All Templates".
• New AI-native templates (informed by the April 2026 CoE notes on AI-native repo patterns — every skeleton ships a concise AGENTS.md, TechDocs site, Dockerfile, and catalog registration):
  • ai-hub-service — provider-agnostic LLM gateway (/healthz, /v1/answer stub, src/providers/ interface)
  • answer-engine-worker — queue consumer + document indexer + query API (/v1/ask, /v1/index), delegates inference to an AI Hub via AI_HUB_URL, answers always carry citations
  • mcp-server — stdio MCP server with ping/echo example tools (@modelcontextprotocol/sdk)

Template consolidation/renames from the PRD were deliberately skipped to avoid scope creep (PRD note: "leave them as-is").

Verification

• yarn lint — clean
• mise run test — 9 passed, 1 skipped (pre-existing suite)
• All template.yaml / catalog YAML parse clean
• All three TS skeletons type-check clean (tsc --noEmit) with their declared deps

Manual QA checklist

• / with no onboarding-tagged entities → Onboarding Docs shows empty state
• / with portal-docs registered → card renders, links to /docs/default/component/portal-docs
• GitHub Light / Dark / Legacy themes → all new sections honour theme
• Mobile ≤600px → cards stack, no horizontal scroll
• /self-service → Recommended group shows all 7 templates; family tags visible
• Scaffold ai-hub-service end-to-end → repo created, entity in catalog, TechDocs builds

Notes

• Curate plugin showcase for templates GitHub and answer engine #86 (plugin showcase for answer engine) is adjacent but not merged here — this PR ships the templates side; plugin/extension curation can stay separate.
• The two pre-existing tsc errors (cli tsconfig lib entry, permission module type annotation) are unrelated to this change.