fix(graph): route wiki/<flat>.md to Type=knowledge, not Type=hall with filename-as-wing

classifyByPath had a hole: paths like wiki/index.md or wiki/<slug>.md
(direct children of wiki/, no subdirectory) hit the default branch and
wrote Wing=parts[1] — which IS the filename, not a wing. Symptom in
brain_entities: rows like (slug=index, wing=index.md) and
(slug=autobe-..., wing=autobe-evaluation-pattern-....md).

Fix: when len(parts) < 3 (no subdirectory at all), fall through to
Type=knowledge and let frontmatter set wing/hall if present.

Add brain/eval/ artifacts at the same time:
- qa-2026-05.md — 20 hand-authored Q→expected-slug pairs covering the
  homelab knowledge corpus across mcp, dex, gitops, postgres, go,
  models, methodology
- score.py — calls brain_query for each pair, scores top-1 + top-3,
  emits per-question detail. BRAIN_MCP_TOKEN via env.

Pre-fix baseline against the live brain: top-1 = 20% (4/20),
top-3 = 65% (13/20). Six hard misses where the expected slug doesn't
even land in the top-5.

Used to gate the phase 2 DIKW redesign (infra#62 follow-up): if
phase 1 fixes (this parser fix + 20 backlink authoring on top
orphans) lift top-1 by <10 absolute points, structure is the
bottleneck and the tier redesign is justified.

ingestion/internal/graph/extract_test.go

@@ -104,3 +104,31 @@ func TestExtract_LineNumbersAre1Indexed(t *testing.T) {
 	require.Len(t, edges, 1)
 	assert.Equal(t, 2, edges[0].SrcLine)
 }
+
+// Files directly under wiki/ (no subdirectory) used to land
+// Type="hall" Wing="<filename>.md" because the path's second segment
+// was the file itself. The fix routes them to Type="knowledge" with
+// empty Wing/Hall and lets frontmatter set them if present.
+func TestExtract_WikiRootFileIsKnowledgeNotHall(t *testing.T) {
+	content := []byte("# Index\n\n- [[foo]]\n")
+	ent, _, ok := Extract("wiki/index.md", content)
+	require.True(t, ok)
+	assert.Equal(t, "index", ent.Slug)
+	assert.Equal(t, "knowledge", ent.Type)
+	assert.Empty(t, ent.Wing)
+	assert.Empty(t, ent.Hall)
+}
+
+func TestExtract_WikiRootFileWithFrontmatterWingHall(t *testing.T) {
+	content := []byte(`---
+wing: homelab
+hall: facts
+---
+# Some root note
+`)
+	ent, _, ok := Extract("wiki/some-note.md", content)
+	require.True(t, ok)
+	assert.Equal(t, "knowledge", ent.Type)
+	assert.Equal(t, "homelab", ent.Wing)
+	assert.Equal(t, "facts", ent.Hall)
+}