feat(topdata): parts autogen from CDN part.yml channel

Phase 2 of the parts-row autogen design: Crucible resolves parts 2DA rows
from the immutable part.yml published with the asset HAK release, over the
anonymous Bunny CDN channel, with the parts consumer required (no fail-open).

- generalize resolveCDNChannelManifest: derive manifest basename + provenance
  label from config; drop hardcoded assets/vfxs.yml so part.yml resolves too
- add filterPartsCDNChannelEntries + mode dispatch implementing the inventory
  contract (restype mdl under part/<cat>/, trailing-digit row id, dedup
  l/r/race/gender variants, sort by source, zero accepted rows = hard fail)
- support hand category + parts/hand dataset mapping (12 datasets total)
- native pipeline: single augment -> normalize -> override sequence with the
  configured parts_rows policy; overrides may update but never synthesize a row
- reject multiple parts_rows consumers in project validation
- tests: parts filter contract, category coverage, offline basename, orphan
  override reject, and a parity guard proving a bare CDN-only parts build

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/topdata/autogen_cdn_channel_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"os"
 	"path/filepath"
 	"testing"
 
@@ -194,6 +195,35 @@ func TestResolveCDNChannelOfflineOverride(t *testing.T) {
 	}
 }
 
+// TestResolveCDNChannelOfflineUsesManifestBasename proves the resolver derives
+// the offline checkout filename from manifest_path's basename (part.yml here),
+// not a hardcoded assets/vfxs.yml, and routes parts_rows through the parts filter.
+func TestResolveCDNChannelOfflineUsesManifestBasename(t *testing.T) {
+	root := testProjectRoot(t)
+	dir := filepath.Join(root, "manifest-checkout")
+	if err := os.MkdirAll(filepath.Join(dir, "assets"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	writeFile(t, filepath.Join(dir, "assets", "part.yml"),
+		"assets:\n  - {path: part/belt/m/pfa0_belt017.mdl, restype: mdl}\n")
+	t.Setenv("SOW_PART_MANIFEST", dir)
+
+	c := projectPartsConsumer()
+	c.Source = project.AutogenSourceConfig{
+		Kind:               "cdn_channel",
+		ManifestPath:       "releases/haks/{tag}/part.yml",
+		OfflineOverrideEnv: "SOW_PART_MANIFEST",
+	}
+
+	m, err := resolveCDNChannelManifest(testProject(root), c, c.Source, nil)
+	if err != nil {
+		t.Fatalf("resolve: %v", err)
+	}
+	if len(m.Entries) != 1 || m.Entries[0].RowID != 17 || m.Entries[0].Group != "belt" {
+		t.Fatalf("unexpected entries: %+v", m.Entries)
+	}
+}
+
 func errorIsUnavailable(err error) bool {
 	return errors.Is(err, errAutogenManifestUnavailable)
 }