fix(brain): unwrap wikilinks that name no entry at the write boundary

Every brain write accepted [[targets]] that resolve to nothing — skill
names, repo names, agent-local memory-file slugs — and each one became a
permanent [high] broken-link finding. The brain-audit digest grew 19 -> 63
high findings between 2026-08-26 and 2026-09-16; 53 of the 63 were exactly
this, and none are fixable by brain-gardener's BrokenLinkFixer, which only
repoints edit-distance-1 renames. There is no target to repoint to.

StripUnresolvedLinks resolves each link against knowledge/ + wiki/ using
brain-gardener's own resolver semantics (bare slug or wing/hall/slug path
form, code spans excluded) and unwraps the misses to plain text, reporting
them as Ref.Unlinked / the MCP `unlinked` field.

Unwrap rather than reject: a refused write on claudewatcher's unattended
ingest path is a lost learning, and the author's words are worth keeping
even when the link is not. An empty corpus is a no-op, so a misconfigured
brainDir cannot strip every link in a note.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ingestion/internal/capture/ports.go

@@ -15,6 +15,10 @@ type Ref struct {
 	Path        string
 	ContentHash string
 	Superseded  bool
+	// Unlinked names the [[wikilink]] targets the store unwrapped to plain
+	// text because they resolve to no entry. Reported rather than rejected:
+	// see brain.StripUnresolvedLinks for why the write still lands.
+	Unlinked []string
 }
 
 // StoredNote is a brain note fetched by Get: the read-after-write