feat: P4 qdrant collection lifecycle (self-heal + guarded rebuild)

- shared TS collection manager: self-heal creates missing collection (1024/cosine)
  and missing keyword payload indexes; never mutates incompatible contracts
  (semantic_index_incompatible); async index visibility polled with bounded deadline
- session admission (qdrantEnsure) uses the manager in self-heal mode; operator path
  keeps require_existing semantics
- runtime lease exposes semanticQdrantUrl to the operator
- operator commands vector-inspect/vector-rebuild with exact confirmation guards
- thothctl workspace vector inspect|rebuild (Go) with --collection/--confirm/--destroy
- p4 acceptance runner: real Qdrant (v1.18.2) lifecycle checks, 11/11 PASS
- docs: CLI contract, manual walkthrough P4 (PENDING), PROJECT_STATE

backend/test/routes-sessions.test.ts

@@ -2476,7 +2476,7 @@ test("POST /sessions proceeds when ollamaEnsure succeeds", async () => {
   });
   const res = await app.inject({ method: "POST", url: "/sessions", payload: { question: "q" } });
   expect(res.json()).toEqual({ id: "s1" });
-  expect(qdrantEnsure).toHaveBeenCalledWith(operationalWorkspace("psd"), 60);
+  expect(qdrantEnsure).toHaveBeenCalledWith(operationalWorkspace("psd"), 60, "self_heal");
   expect(ensureWs).toContain(`/snapshots/${"e".repeat(40)}/psd.yaml`);
 });