feat: Learning page — capability timeline + trend, built on real data

The plan's "learning view" (runbook success-rate trends, promoted
skills, capability timeline) assumes the patterns/skills/feedback
pipeline is populated. It isn't: all three tables are empty in
production and nothing in the codebase ever writes to feedback, so
building the UI against them today would ship a permanently-empty
page. Scoped instead around data that's real and growing —
executions — while still wiring up /patterns and /skills so the page
needs no rework once that pipeline exists.

New /api/v1/learning/timeline (per-verb first-success date + success
rate, parsed via the existing splitAction helper) and
/api/v1/learning/trend (30-day daily success/fail counts), both
read-only queries against executions. Patterns and skills sections
call the existing (untouched) ListPatterns/ListSkills endpoints and
render an explanatory empty state instead of nothing.

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

internal/httpapi/server.go

@@ -150,6 +150,12 @@ func NewHandler(ctx context.Context, pool *db.Pool, cfg config.Config, uiHandler
 	r.With(combinedAuth(cfg)).Get("/api/v1/activity/recent", s.serveRecentActivity)
 	r.With(combinedAuth(cfg)).Get("/api/v1/activity/session/{id}", s.serveSessionDigest)
 
+	// Learning view: capability timeline + success trend, both derived from
+	// executions (real, growing data) rather than the patterns/skills tables,
+	// which are correctly modeled but have no writers anywhere yet.
+	r.With(combinedAuth(cfg)).Get("/api/v1/learning/timeline", s.serveLearningTimeline)
+	r.With(combinedAuth(cfg)).Get("/api/v1/learning/trend", s.serveLearningTrend)
+
 	// Mount MCP at /mcp (plan R3-10)
 	nomosAgentID := uuid.Nil
 	if cfg.NomosAgentID != "" {