cleanup: bump qwen2.5 → qwen3.5:latest in active defaults

stronger local rung is now the small-model-pipeline tier-1 default
across both Rust legacy + Go rewrite (cf. golangLAKEHOUSE phase 1).
same JSON-clean property as qwen2.5, more capacity. ollama still
serves both side-by-side; rollback is a 4-line revert if a workload
regresses.

active-default sites:
- lakehouse.toml [ai] gen_model + rerank_model → qwen3.5:latest
- mcp-server/observer.ts diagnose call (Phase 44 /v1/chat path) → qwen3.5:latest
- mcp-server/index.ts model roster doc → qwen3.5:latest first
- crates/vectord/src/rag.rs ContinuableOpts + RagResponse.model → qwen3.5:latest

skipped: execution_loop/mod.rs comments describing historic qwen2.5
tool_call quirks — those are documentation of past behavior, not
active defaults. data/_catalog/profiles/*.json are runtime-generated
(gitignored), not in scope for tracked changes.

cargo check -p vectord: clean. no behavioral change in the audit
pipeline — same JSON-clean local model, same think=Some(false)
posture, just stronger upstream.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/vectord/src/rag.rs

@@ -163,7 +163,11 @@ pub async fn query(
     // production caller of the Phase 21 primitives — see audit finding
     // "Phase 21 Rust primitives are wired but not CALLED by any
     // production surface" from 2026-04-21.
-    let mut cont_opts = ContinuableOpts::new("qwen2.5:latest");
+    // 2026-04-30 model bump: qwen2.5:latest → qwen3.5:latest to match
+    // the small-model-pipeline local-tier default. Same JSON-clean
+    // property, more capacity. think=Some(false) preserved — RAG hot
+    // path doesn't need reasoning traces; direct answers only.
+    let mut cont_opts = ContinuableOpts::new("qwen3.5:latest");
     cont_opts.max_tokens = Some(512);
     cont_opts.temperature = Some(0.2);
     cont_opts.shape = ResponseShape::Text;
@@ -176,7 +180,7 @@ pub async fn query(
         // echoes whatever Ollama loaded). Use the configured tier model
         // for now; if RAG needs to report the actual resolved model,
         // the runner can add a post-call ps probe later.
-        model: "qwen2.5:latest".to_string(),
+        model: "qwen3.5:latest".to_string(),
         sources: results,
         tokens_generated: None,
     })