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>

web/src/lib/api.ts

@@ -277,6 +277,72 @@ export async function fetchSessionDigest(sessionId: string): Promise<SessionDige
   return res.json()
 }
 
+export interface CapabilityTimelineItem {
+  verb: string
+  first_success: string | null
+  successes: number
+  total: number
+}
+
+export async function fetchLearningTimeline(): Promise<CapabilityTimelineItem[]> {
+  const res = await fetch(`${API}/learning/timeline`)
+  if (!res.ok) return []
+  const data = await res.json()
+  return data.items ?? []
+}
+
+export interface TrendBucket {
+  day: string
+  successes: number
+  failures: number
+}
+
+export async function fetchLearningTrend(): Promise<TrendBucket[]> {
+  const res = await fetch(`${API}/learning/trend`)
+  if (!res.ok) return []
+  const data = await res.json()
+  return data.items ?? []
+}
+
+export interface Pattern {
+  id: string
+  slug: string
+  applies_type: string
+  action: string
+  pattern: string
+  confidence: number
+  evidence_count: number
+  success_count?: number
+  failure_count?: number
+  status: string
+  quarantined?: boolean
+}
+
+export async function fetchPatterns(): Promise<Pattern[]> {
+  const res = await fetch(`${API}/patterns`)
+  if (!res.ok) return []
+  const data = await res.json()
+  return data.items ?? []
+}
+
+export interface Skill {
+  id: string
+  slug: string
+  name: string
+  applies_type?: string | null
+  action: string
+  status: string
+  success_rate?: number | null
+  last_used_at?: string | null
+}
+
+export async function fetchSkills(): Promise<Skill[]> {
+  const res = await fetch(`${API}/skills`)
+  if (!res.ok) return []
+  const data = await res.json()
+  return data.items ?? []
+}
+
 export interface Signal {
   id: string
   slug: string