Fix post-merge wiki gaps

[lucarlig]

Summary

• document the MCP 2026-07-28 Origin/Host validation middleware and allowlist behavior
• restore the complete CLI/environment reference and remove obsolete backend transport fields
• document the current control-plane/dataplane authentication split, request flow, authorization boundary, and revocation gap
• require mdBook validation for docs-only changes and add the testing page to the wiki index
• make AGENTS.md require terse, factual, compact, agent-oriented wiki content and remove stale book wording

Why

The documentation conflicts resolved during #72 dropped newer knowledge already present on main, leaving the new single source of truth incomplete and, in places, inaccurate. Commits c16a6bf and f7123b2 were also audited: most useful content was already present, while the remaining deployment Origin/CORS clarification was carried forward here.

Impact

Documentation only. The wiki now matches the current request middleware, configuration model, Streamable HTTP-only backend contract, control-plane publisher/API-token behavior, and dataplane JWT/config enforcement. Agent instructions now keep future wiki updates compact and retrieval-focused.

Validation

• mdbook build _context/wiki
• mdbook test _context/wiki
• inspected the rendered headings, tables, validation commands, and index links
• cargo run --locked -p contextforge-data-plane --bin contextforge-data-plane -- --help
• compared authentication documentation with the dataplane claims/config layers and the pinned control-plane publisher/token implementation
• verified AGENTS.md contains no stale book references
• repository pre-commit hooks

[Lang-Akshay]

LGTM