Add Home page, matching platform-main's wiki landing-page pattern
Verify wiki against real code; consolidate into hosted diagrams
Accuracy pass: added missing ClickHouse coverage throughout, corrected
the SSL model (one CA per server, reused across its databases, not
one CA per database), fixed React 18->19 and fabricated
testing-convention/React-feature claims that didn't match this
codebase, and replaced Testing Strategy's fictional 4-layer framework
with the real Pest/Vitest/Playwright approach.
Consolidated 16 pages into short blurbs pointing at 4 new hosted
diagrams (system-architecture.html, deployment-pipeline.html,
database-provisioning-engines.html, env-vars-and-volumes.html) instead
of each page duplicating the same content - including all 8 per-engine
StartAction pages, which repeated a near-identical lifecycle diagram.
SSL Subsystem, React 19 Migration, and Testing Strategy stayed as
short pages pointing to their own canonical source rather than being
deleted outright. Removed the placeholder Home.md. Every link uses the
real filename instead of a paraphrase.