Add MCP server, note mutation endpoint, and updated_at tracking (v3.0.0)

New MCP server (mcp/) exposes kb operations as native MCP tools over
Streamable HTTP with Bearer token auth. Supports collections via tag
conventions, chunked file uploads, and agent-side search patterns.

Engine gains PATCH /api/v1/notes/{id} for in-place note updates with
transactional re-chunk/re-embed, and updated_at column on documents.

Go client adds updatenote command and Patch HTTP method.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SKILL.md

@@ -158,6 +158,30 @@ Use filters when the question implies a specific domain:
 - From a specific topic → `--tags <topic>`
 - Check available tags first: `kb tags --format json`
 
+## Updating notes
+
+```bash
+kb updatenote 42 "revised note content"           # update note by ID
+```
+
+Updates the text of an existing note in place, preserving its ID, creation timestamp, and tags. Re-chunks and re-embeds the new text.
+
+## MCP server (agent integration)
+
+For agent-to-agent integration, kb provides an MCP server alongside the CLI. The MCP server
+exposes the same operations as native MCP tools over Streamable HTTP transport, which agents
+can connect to directly without subprocess overhead.
+
+**MCP tools:** `kb_search`, `kb_addnote`, `kb_update_note`, `kb_get`, `kb_status`, `kb_jobs`,
+`kb_upload_start`, `kb_upload_chunk`, `kb_upload_finish`.
+
+The MCP server supports **collections** — scoped document namespaces (e.g. `memory`, `documents`,
+`workspace`) implemented via tag conventions. This is the recommended way for agents to separate
+their memory from user documents.
+
+If the kb engine is already running via Docker Compose, add the MCP server by deploying the
+`kb-mcp` service from the same compose file. Agents connect to it on port 3000 (default).
+
 ## Important notes
 
 - Always use `--format json` for machine parsing