feat: launch Stripe billing flows with lifecycle hardening and analytics

add Stripe checkout, portal, webhook ingestion, and idempotent event persistence

add billing lifecycle state (grace/sync/timeline/admin visibility) and stronger entitlement handling

add analytics event tracking and admin summary APIs plus account/pricing UI integration

db/migrations/0006_analytics_events.sql

@@ -0,0 +1,20 @@
+create table if not exists public.analytics_events (
+  id uuid primary key default gen_random_uuid(),
+  event_name text not null,
+  event_source text not null check (event_source in ('web_app', 'api', 'stripe_webhook', 'system')),
+  user_id uuid references public.users (id) on delete set null,
+  workspace_id uuid references public.workspaces (id) on delete set null,
+  plan_code text,
+  addon_code text,
+  resource text,
+  amount numeric,
+  currency text,
+  metadata_json jsonb not null default '{}'::jsonb,
+  occurred_at timestamptz not null default now(),
+  created_at timestamptz not null default now()
+);
+
+create index if not exists analytics_events_occurred_at_idx on public.analytics_events (occurred_at desc);
+create index if not exists analytics_events_event_name_idx on public.analytics_events (event_name);
+create index if not exists analytics_events_workspace_id_idx on public.analytics_events (workspace_id);
+create index if not exists analytics_events_plan_code_idx on public.analytics_events (plan_code);