docs: sync docs and codemap with current behaviour

[kevintseng]

Brings the docs back in line with current behaviour.

• CODEMAP: corrected hook descriptions, storage and core module lists, dashboard entry point.
• API reference and architecture: import keeps archive state only from the CLI; forget responses per transport; /v1/projects, /v1/entities, /v1/health details; missing CLI commands and fields.
• Install guide, READMEs and platform guides: MEMESH_PROJECT_ROOT for MCP-only clients; prompt templates send why with decisions and tag the exact project id; memories without a project tag can appear in every project's briefing.
• memesh skill: current message notice name; MCP project parameter; replace rules.
• Changelog: missing entries added.

Closes #599