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/parity_guard_test.go

@@ -1,6 +1,8 @@
 package topdata
 
 import (
+	"os"
+	"path/filepath"
 	"testing"
 
 	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/project"
@@ -54,3 +56,45 @@ func TestParityGuardCDNChannelProducesAccessoryRows(t *testing.T) {
 		t.Fatalf("PARITY GUARD: expected lock id for %s, got %#v", wantKey, got[0].LockData)
 	}
 }
+
+// PARITY GUARD (parts): a bare project whose only parts source is the offline
+// CDN-equivalent (SOW_PART_MANIFEST -> a part.yml), with no NWN_ROOT, no token,
+// no asset checkout, must produce parts rows from the filtered inventory. If
+// parts resolution ever drifts back into a wrapper, this fails.
+func TestParityGuardCDNChannelProducesPartsRows(t *testing.T) {
+	root := testProjectRoot(t)
+	checkout := filepath.Join(root, "manifest-checkout")
+	if err := os.MkdirAll(filepath.Join(checkout, "assets"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	writeFile(t, filepath.Join(checkout, "assets", "part.yml"),
+		"assets:\n  - {path: part/belt/m/pfa0_belt017.mdl, restype: mdl}\n  - {path: part/belt/m/pfa0_belt018.mdl, restype: mdl}\n")
+	t.Setenv("SOW_PART_MANIFEST", checkout)
+	t.Setenv("NWN_ROOT", "")
+
+	c := projectPartsConsumer()
+	c.Source = project.AutogenSourceConfig{
+		Kind:               "cdn_channel",
+		ChannelsPath:       "releases/haks/channels.json",
+		ManifestPath:       "releases/haks/{tag}/part.yml",
+		ReleaseMarkerPath:  "releases/haks/{tag}/haks.json",
+		OfflineOverrideEnv: "SOW_PART_MANIFEST",
+	}
+
+	p := testProject(root)
+	p.Config.Autogen.Consumers = []project.AutogenConsumerConfig{c}
+
+	collected := []nativeCollectedDataset{partsDatasetWithIDs("parts/belt", nil)}
+
+	got, err := applyAutogenConsumers(p, collected, nil)
+	if err != nil {
+		t.Fatalf("applyAutogenConsumers failed: %v", err)
+	}
+	ids := map[int]bool{}
+	for _, row := range got[0].Rows {
+		ids[row["id"].(int)] = true
+	}
+	if !ids[17] || !ids[18] {
+		t.Fatalf("PARITY GUARD: expected belt rows 17 and 18 from inventory, got %#v", got[0].Rows)
+	}
+}