feat(pricing): rip 14-day trial, add activity-based auto-pause foundation

Author: ryanwaits

.changeset/pricing-sprint-a.md

@@ -0,0 +1,12 @@
+---
+"@secondlayer/shared": minor
+"@secondlayer/cli": patch
+---
+
+Pricing foundation (Sprint A) — switch from 14-day trial to activity-based auto-pause, org-level billing prep.
+
+- Migration 0046 drops `tenants.trial_ends_at` + index, adds `tenants.last_active_at timestamptz NOT NULL DEFAULT now()` with index `(plan, last_active_at) WHERE status = 'active'`
+- Migration 0047 adds nullable `tenant_id` to `usage_daily` (+ best-effort backfill for single-tenant accounts), widens the unique key to `(account_id, tenant_id, date)` so Sprint-C Stripe metering can bill per-tenant
+- `TrialExpiredError` + `TRIAL_EXPIRED` code dropped (dead after trial removal)
+- New `bumpTenantActivity(slug)` + `listIdleHobbyTenants(idleSince)` query helpers
+- CLI drops trial-days-left from `sl instance info` and `sl whoami`, drops `TRIAL_EXPIRED` handlers