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/6_ui.md

@@ -1,5 +1,13 @@
 # UI Surfaces
 
+## Workspace Model
+
+RA-H OS follows the current pane model:
+- explicit `1 / 2 / 3` visible panes
+- chat anchored to the right edge of the active workspace
+- node tabs only in node panes
+- singleton non-node panes
+
 ## Main Views
 
 - `Feed` for recent and sortable node browsing
@@ -12,12 +20,12 @@
 ## UI Contract After The Migration
 
 - The app no longer exposes a dimensions pane.
-- Feed and table filtering are context-aware and no longer dimension-based.
+- Feed and table filtering are not dimension-based.
 - Persisted pane layout should only hydrate valid pane types: `views`, `node`, `contexts`, `map`, `table`, `skills`.
 - Contexts are shown as a secondary organizational aid, not as a hard requirement for capture.
 
 ## Focus And Capture
 
-- Capture must succeed when both context and dimensions are omitted.
+- Capture must succeed when context is omitted.
 - Focus surfaces should emphasize title, description, source, metadata, and edges.
 - Node cards may show context when present, but should not depend on it for meaning.