fix(pipeline): same-named sources in two wings, entity/source slug clashes, model-chosen types (review of #211)

- a source whose slug is taken by anything but this wing's own page gets a
  wing-qualified, stable slug (talk-homelab) instead of failing the ingest
- an extracted entity/concept whose slug belongs to a different page is skipped
  with a warning, so one page can no longer lock a source out of re-ingest
- in a wing only source/concept/entity are valid page types; the model (and so
  the clip) can no longer choose wiki/<type>/ directories
Mutation-checked; stable-slug choice pinned directly because title resolution
masks it at the Run level.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ingestion/internal/pipeline/build.go

@@ -28,7 +28,7 @@ func BuildPagesIn(wing string, rawPages []RawPage, sourceSlug, date string) ([]w
 	for _, rp := range rawPages {
 		// The type becomes a directory under wiki/; "../raw" wrote outside it
 		// (PR #147 review). Only a plain lower-case name is a page type.
-		if !validPageType.MatchString(rp.Type) {
+		if !validPageType.MatchString(rp.Type) || (wing != "" && !layoutType(rp.Type)) {
 			warnings = append(warnings, fmt.Sprintf("skipped page with invalid type %q", rp.Type))
 			continue
 		}
@@ -42,6 +42,11 @@ func BuildPagesIn(wing string, rawPages []RawPage, sourceSlug, date string) ([]w
 	return out, warnings
 }
 
+// layoutType reports whether a wing-mode page type has a place in the layout.
+// The type comes from the model, so from the clip being ingested: anything else
+// would name a directory (wiki/<type>/) of the model's choosing.
+func layoutType(t string) bool { return t == "source" || t == "concept" || t == "entity" }
+
 var validPageType = regexp.MustCompile(`^[a-z][a-z0-9-]*$`)
 
 func computeSlug(rp RawPage, sourceSlug string) string {