feat: finalize local OpenAI key flow and MCP docs

- add server-side .env.local OpenAI key management for the open-source app
- route AI features through the preferred local key path and lazy-load embed recovery
- rewrite README and docs for current MCP setup, schema, and fully-local guidance

Generated with Claude Code

docs/9_open-source.md

@@ -1,12 +1,43 @@
 # Open Source Surface
 
-The open-source RA-H surface should match the main app contract:
+The open-source RA-H surface should match the main app contract where product behavior is shared:
 
 - no runtime `dimensions` model,
 - optional soft `contexts`,
 - no automatic context assignment on write,
 - node quality driven by title, description, source, metadata, and edges.
 
+## What RA-H OS Includes
+
+- local SQLite graph
+- local UI
+- standalone MCP server
+- shared skills system
+- BYO API key path
+
+## What RA-H OS Does Not Promise
+
+- every private-app surface
+- private subscription/auth behavior
+- official support for every local model stack or vector backend someone can wire up
+- a guarantee that every community setup is first-class supported
+
+## Support Boundary
+
+Supported core path:
+- RA-H OS app
+- local SQLite
+- standard standalone MCP server
+- documented repo install flow
+
+Reasonable community pattern:
+- local model or alternate MCP-capable chat surface layered on top of the documented contract
+
+Experimental / user-owned:
+- custom vector backends
+- unsupported deployment targets
+- aggressive local-model substitutions that degrade tool quality
+
 ## Important App Routes
 
 - `app/api/nodes/`