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record with a superseded note -- the feature shipped and is documented,
just no longer current behaviour.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

specs/capture-bdd-spec.md

@@ -2,6 +2,8 @@
 
 **Status:** Decisions resolved 2026-06-22 (§4). Ready for implementation scoping. `capture` is a
 privileged cross-harness write path touching brain + Gitea + ai-sessions.
+**Superseded 2026-07-27:** the ai-sessions summary write path specified below was removed post-ship
+(see `specs/capture-implementation-report.md`). `capture` now touches brain + Gitea only.
 **Tracks:** hyperguild #49.
 **Governed by:** `infra/docs/architecture/01-invariants.md` (I1–I5), the admissibility test in
 `00-synthesis-model.md`, and the distributed-consolidation shape mandated by