v0.3.0 finish: TUI tests, embedding wiring, gateway :configured, focus commands, export cleanup

- TUI: Fix stale contract (remove handle-return/*incoming-msgs*), rewrite
  10->13 tests (38 checks, 100% pass). Export missing symbols from TUI
  package. Fix view-chat contract arity.
- Gateway messaging: Add :configured key to registry (boolean, nil default).
  Fix contract to match (vault-based, not env-var-based).
- Async Embedding Gateway: Add *embedding-backend* var, embeddings-compute
  function. Modify ingest-ast to populate vectors on new objects.
  Add EMBEDDING_PROVIDER env var support. Add Contract + 4 tests (8 checks).
- Context Manager: Add /focus, /scope, /unfocus commands to TUI on-key
  handler. Commands degrade gracefully when context-manager not loaded.
- Export hygiene: Remove 30+ ghost exports (undefined symbols). Remove
  duplicate/mismatched names. Exports now match actual definitions.

org/gateway-tui-view.org

@@ -10,12 +10,13 @@ State is read via ~(st :key)~ — no mutation here.
 
 1. (view-status win): renders the status bar with connection info,
    version, and timestamp.
-2. (view-chat win): renders the scrolled chat message list. Messages
-   are color-coded: green (user), white (agent), yellow (system).
+2. (view-chat win h): renders the scrolled chat message list. Takes
+   window and available height. Messages are color-coded: green (user),
+   white (agent), yellow (system).
 3. (view-input win): renders the input line with cursor and typing
    indicator.
-4. (redraw scr chat-win status-win input-win): dispatches redraws
-   based on ~(st :dirty)~ flags. Minimizes terminal writes.
+4. (redraw sw cw ch iw): dispatches redraws based on ~(st :dirty)~
+   flags (status, chat, input). Minimizes terminal writes.
 
 ** Status Bar
 #+begin_src lisp