feat(capture): remove summary->ai-sessions write path

ai-sessions#13: capture's `summary` field wrote a frontmatter shape
(title/harness/fidelity/captured_at/repos_touched) that ai-sessions'
own extract/audit pipeline can't parse -- silently invisible to that
repo's own audit tooling, and bypassing its redaction + Stage2
completeness gates by construction. Only 5 files ever landed this way
over 3 weeks; the summary capability's whole value (speed) fights
ai-sessions' whole value (redacted, audited, complete), so kill it
rather than build a second parse branch.

capture now persists insights -> brain and action items -> Gitea
tickets only. Removes Summary/SummaryResult/SummaryWriter and all
wiring (service, REST body, MCP tool schema); close-session updated to
stop assembling a summary payload. specs/capture-*.md kept as historical
record with a superseded note -- the feature shipped and is documented,
just no longer current behaviour.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WPdSHbp9Utb2hPFm9wDG59

ingestion/internal/capturehttp/handler_test.go

@@ -49,7 +49,7 @@ func newHandler(t *testing.T, v capturehttp.Validator, tr capture.IssueTracker,
 	t.Helper()
 	cfg, err := classification.Load(t.TempDir())
 	require.NoError(t, err)
-	svc := capture.NewService(brainstore.New(t.TempDir()), tr, nil, cfg, audit.NewSlogSink(nil))
+	svc := capture.NewService(brainstore.New(t.TempDir()), tr, cfg, audit.NewSlogSink(nil))
 	return capturehttp.New(svc, v, staticTok, "local-cli", capturehttp.NewOriginResolver(sovereign))
 }
 
@@ -190,7 +190,7 @@ func (refusingAudit) Record(context.Context, capture.AuditEntry, capture.AuditOu
 func TestAuditUnavailableIs503(t *testing.T) {
 	cfg, err := classification.Load(t.TempDir())
 	require.NoError(t, err)
-	svc := capture.NewService(brainstore.New(t.TempDir()), fakeTracker{}, nil, cfg, refusingAudit{})
+	svc := capture.NewService(brainstore.New(t.TempDir()), fakeTracker{}, cfg, refusingAudit{})
 	h := capturehttp.New(svc, nil, staticTok, "local-cli", capturehttp.NewOriginResolver(nil))
 
 	rr := do(t, h, "Bearer "+staticTok, internalReq())