feat: add userName tracking to audit events

- Add userName column to AuditEvent schema with index and migration
- Add GET /api/v1/auth/me endpoint returning current user identity
- AuditCollector auto-fills userName from session→user map, resolved
  lazily via /auth/me on first session creation
- Support userName and date range (from/to) filtering on audit events
  and sessions endpoints
- Audit console sidebar groups sessions by project → user
- Add date filter presets (d key: all/today/1h/24h/7d) to console
- Add scrolling and page up/down to sidebar navigation
- Tests: auth-me (4), audit-username collector (4), route filters (2),
  smoke tests (2)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/db/prisma/migrations/20260304120000_add_audit_username/migration.sql

@@ -0,0 +1,5 @@
+-- AlterTable
+ALTER TABLE "AuditEvent" ADD COLUMN     "userName" TEXT;
+
+-- CreateIndex
+CREATE INDEX "AuditEvent_userName_idx" ON "AuditEvent"("userName");