feat: global activity feed + session digest

Ops "Executions" tab showed raw target UUIDs, alphabetical (not
recency) order, and a stale status vocabulary from an earlier schema
iteration — never actually usable as a live "what's happening" view.
Replaced with a new recency-ordered /api/v1/activity/recent endpoint
and matching table (human-readable action summaries, risk/status
badges, duration, inline error preview).

Also added /api/v1/activity/session/{id} + a collapsible SessionDigest
panel in the chat rail, answering "what did this session actually do"
(executions by status, entities touched, knowledge written) — the
missing piece for proactive outcome reporting to be visible in the UI,
not just in the chat transcript.

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

internal/httpapi/server.go

@@ -144,6 +144,12 @@ func NewHandler(ctx context.Context, pool *db.Pool, cfg config.Config, uiHandler
 	// HandlerWithOptions so it wins over any generated catch-all.
 	r.With(combinedAuth(cfg)).Get("/api/v1/knowledge/recent", s.serveRecentKnowledge)
 
+	// Custom (non-OpenAPI) routes: the global activity feed (recency-ordered,
+	// unlike ListExecutions which sorts by target for pagination) and the
+	// per-session "what did this session do" digest.
+	r.With(combinedAuth(cfg)).Get("/api/v1/activity/recent", s.serveRecentActivity)
+	r.With(combinedAuth(cfg)).Get("/api/v1/activity/session/{id}", s.serveSessionDigest)
+
 	// Mount MCP at /mcp (plan R3-10)
 	nomosAgentID := uuid.Nil
 	if cfg.NomosAgentID != "" {