REUSE-WP-0018-T03: LLM semantic rerank for plan-check

llm-connect came up locally (mock provider, 127.0.0.1:8080), unblocking
this task.

reuse_surface/plan_check.py: build_rerank_prompt/request_rerank/apply_rerank,
reusing llm_bridge.execute_prompt/extract_json_object (same pattern as
maintain_llm.py's request_maintain_patches). New schema
schemas/plan-check-rerank.schema.json rejects malformed responses (missing
fields, non-JSON, invented candidate ids outside the input set) rather than
guessing.

Per design principle 3 (deterministic matches always rank first),
apply_rerank appends LLM-scored entries after the deterministic list
(kind: 'llm') instead of reordering it -- the trusted base result is
identical with or without the rerank pass. Graceful skip via a 'notes'
field when LLM_CONNECT_URL is unset or the response is malformed, mirroring
maintain.py's no_llm/skip pattern. New --llm-url/--no-llm CLI flags.

Also extended plan-check-result.schema.json for 'notes' and the
(pre-existing, previously unschema'd) 'filed_capability_request' field.

9 new pytest cases; 89 total pass. Live-verified against the running
llm-connect instance: it correctly rejected the mock provider's non-JSON
response and surfaced the skip note, with the deterministic verdict and
match order completely unaffected.

REUSE-WP-0018 is now fully done (T01-T06). Updated
docs/IntentScopeGapAnalysis.md priority 29 to Closed and the workplan's
own frontmatter status to finished.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

schemas/plan-check-rerank.schema.json

@@ -0,0 +1,27 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://reuse-surface.local/schemas/plan-check-rerank.schema.json",
+  "title": "PlanCheckRerankResponse",
+  "description": "T03 LLM rerank response. The model may only score/reorder candidate IDs it was given -- it must not invent new ones. plan_check.py enforces that separately from this schema (schema can't see the input candidate set).",
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["candidates"],
+  "properties": {
+    "candidates": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": ["id", "confidence"],
+        "properties": {
+          "id": {
+            "type": "string",
+            "pattern": "^capability\\.[a-z0-9]+(\\.[a-z0-9-]+)+$"
+          },
+          "confidence": {"type": "number", "minimum": 0, "maximum": 1},
+          "rationale": {"type": "string"}
+        }
+      }
+    }
+  }
+}