refactor(db): drop the runtime schema mirror

ensureDbCompatibility ran ALTER TABLE / CREATE TABLE IF NOT EXISTS on the
login, register, token and session paths, mirroring columns every
migration under prisma/migrations already creates. The entrypoint applies
those migrations before the server listens and stops the boot when one
fails, so the mirror never had work to do, and DDL on a request path
needs the table's owner: a connection that may only read and write rows
fails every login on it. Drop the module, its call sites and the mocks
that stubbed it out.

src/app/api/admin/import-apple-health-export/__tests__/route.test.ts

@@ -12,9 +12,6 @@ vi.mock("@/lib/auth/audit", () => ({
   auditLog: vi.fn().mockResolvedValue(undefined),
 }));
 vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
-vi.mock("@/lib/db-compat", () => ({
-  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
-}));
 vi.mock("next/headers", () => ({
   headers: vi.fn(async () => ({ get: () => null })),
   cookies: vi.fn(async () => ({

src/app/api/admin/maintenance/measurements/__tests__/status.test.ts

@@ -12,9 +12,6 @@ vi.mock("@/lib/auth/audit", () => ({
   auditLog: vi.fn().mockResolvedValue(undefined),
 }));
 vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
-vi.mock("@/lib/db-compat", () => ({
-  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
-}));
 vi.mock("next/headers", () => ({
   headers: vi.fn(async () => ({ get: () => null })),
   cookies: vi.fn(async () => ({

src/app/api/admin/maintenance/pulse-day-mean/__tests__/route.test.ts

@@ -18,9 +18,6 @@ vi.mock("@/lib/auth/audit", () => ({
 }));
 vi.mock("@/lib/jobs/boss-instance", () => ({ getGlobalBoss: vi.fn() }));
 vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
-vi.mock("@/lib/db-compat", () => ({
-  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
-}));
 vi.mock("next/headers", () => ({
   headers: vi.fn(async () => ({ get: () => null })),
   cookies: vi.fn(async () => ({

src/app/api/admin/settings/assistant-flags/__tests__/route.test.ts

@@ -15,9 +15,6 @@ vi.mock("@/lib/auth/audit", () => ({
   auditLog: vi.fn().mockResolvedValue(undefined),
 }));
 vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
-vi.mock("@/lib/db-compat", () => ({
-  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
-}));
 vi.mock("next/headers", () => ({
   headers: vi.fn(async () => ({ get: () => null })),
   cookies: vi.fn(async () => ({

src/app/api/admin/settings/module-availability/__tests__/route.test.ts

@@ -15,9 +15,6 @@ vi.mock("@/lib/auth/audit", () => ({
   auditLog: vi.fn().mockResolvedValue(undefined),
 }));
 vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
-vi.mock("@/lib/db-compat", () => ({
-  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
-}));
 vi.mock("next/headers", () => ({
   headers: vi.fn(async () => ({ get: () => null })),
   cookies: vi.fn(async () => ({