feat(graph): cross-wing tunnels by shared topics (#1180)

When two wings have one or more confirmed TOPIC labels in common, the
miner now drops a symmetric tunnel between them at mine time so the
palace graph reflects shared themes (frameworks, vendors, recurring
concepts).

- llm_refine: TOPIC label routes to a dedicated `topics` bucket so the
  signal survives confirmation instead of getting collapsed into
  `uncertain` and dropped.
- entity_detector / project_scanner: bucket plumbed through the
  detection pipeline; `confirm_entities` returns confirmed topics
  alongside people/projects.
- miner.add_to_known_entities: optional `wing` parameter records the
  confirmed topics under `topics_by_wing` in
  `~/.mempalace/known_entities.json`. Wing names do NOT leak into the
  flat known-name set used by drawer-tagging.
- palace_graph: `compute_topic_tunnels` and `topic_tunnels_for_wing`
  create symmetric tunnels via the existing `create_tunnel` API so they
  share dedup and persistence with explicit tunnels.
- miner.mine: post-file-loop pass calls `topic_tunnels_for_wing` for
  the freshly-mined wing. Failures are logged but never abort the mine.
- config: `topic_tunnel_min_count` knob (env
  `MEMPALACE_TOPIC_TUNNEL_MIN_COUNT` or `~/.mempalace/config.json`),
  default 1.

Tests cover topic persistence through init->mine, tunnel creation when
wings share a topic, no tunnel below threshold, cross-wing tunnel
retrieval via `list_tunnels`, dedup on recompute, case-insensitive
overlap, and the end-to-end mine-time wiring.

Out of scope for this PR (called out in the PR body): manifest-
dependency overlap, per-topic allow/deny lists, search-result surfacing.

tests/test_project_scanner.py

@@ -363,11 +363,14 @@ def test_to_detected_dict_shape():
     projects = [ProjectInfo(name="p", repo_root=Path("."), is_mine=True, manifest="package.json")]
     people = [PersonInfo(name="Jane Doe", total_commits=5, repos={"r"})]
     d = to_detected_dict(projects, people)
-    assert set(d.keys()) == {"people", "projects", "uncertain"}
+    # ``topics`` is the LLM-refine bucket for cross-wing tunnel signal —
+    # always present even when empty so callers can rely on the shape.
+    assert set(d.keys()) == {"people", "projects", "topics", "uncertain"}
     assert d["projects"][0]["name"] == "p"
     assert d["projects"][0]["type"] == "project"
     assert d["people"][0]["name"] == "Jane Doe"
     assert d["people"][0]["type"] == "person"
+    assert d["topics"] == []
     assert d["uncertain"] == []