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record with a superseded note -- the feature shipped and is documented,
just no longer current behaviour.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/cmd/server/main.go

@@ -457,12 +457,8 @@ func main() {
 			os.Exit(1)
 		}
 		auditSink := buildAuditSink(ctx, brainDir, logger)
-		// The Gitea client also satisfies SummaryWriter (#66): session
-		// summaries are written to mathias/ai-sessions over the same API
-		// token. nil only if a future tracker impl lacks file writes.
-		summaryWriter, _ := tracker.(capture.SummaryWriter)
 		captureSvc := capture.NewService(
-			mcpSrv.BrainStore(), tracker, summaryWriter, classCfg, auditSink)
+			mcpSrv.BrainStore(), tracker, classCfg, auditSink)
 		sovereign := splitList(os.Getenv("BRAIN_CAPTURE_SOVEREIGN_PRINCIPALS"))
 		resolver := capturehttp.NewOriginResolver(sovereign)
 		captureH := capturehttp.New(captureSvc, jwtValidator, mcpToken, "local-cli", resolver)