feat(topdata): parts autogen from CDN part.yml channel (Phase 2) (#25)

Phase 2 of the parts-row autogen design — Crucible (sow-tools) side only.

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).

## Changes
- **Resolver (T3):** generalize \`resolveCDNChannelManifest\` — derive manifest basename + provenance label from config; drop hardcoded \`assets/vfxs.yml\` so \`part.yml\` resolves through the same path. VFX behavior unchanged.
- **Parts filter (T4):** \`filterCDNChannelEntries\` dispatches on consumer mode; new \`filterPartsCDNChannelEntries\` implements the inventory contract — \`restype: mdl\` under \`part/<supported-cat>/\`, row id from trailing digits, dedup l/r/race/gender variants by (category,rowID), sort by source, **zero accepted rows = hard fail**, reject row id 0 / non-numeric / malformed / no-assets.
- **Category (T5):** add \`hand\` + \`parts/hand\` mapping (12 datasets; \`leg→legs\` already present).
- **Pipeline (T6):** native build runs one explicit augment → normalize → override sequence under the configured \`parts_rows\` policy; overrides may update an existing/discovered row but **never synthesize** one (orphan override now errors).
- **Validation (T7):** reject more than one \`parts_rows\` consumer.

## Tests
9 new tests: parts filter contract, 12-dataset coverage, offline manifest-basename, orphan-override reject + discovered-row update, and a parity guard proving a bare CDN-only parts build needs no wrapper/token/NWN_ROOT/checkout.

Gate green: \`go test ./internal/topdata/... ./internal/project/...\` + full \`go build ./... && go test ./...\`.

## Scope / ordering
Phase 2 is inert until **Phase 1** (sow-assets-manifest publishes \`part.yml\`) ships and the operational **Gate** (release publish/promote) runs, then **Phase 3** enables the sow-topdata consumer. Do not enable the consumer against a channel whose current release predates \`part.yml\`.

Plan: \`sow-topdata/docs/superpowers/plans/2026-06-25-topdata-parts-autogen-channel.md\`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #25
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.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)
 }