test(ci): add quality gates, e2e data prep, and i18n integration coverage

docs/product-engineering/testing-strategy.md

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+# Testing Strategy Baseline
+
+## Goals
+
+- Keep lint, typecheck, unit/integration, and e2e as mandatory quality gates.
+- Make e2e runs deterministic by preparing schema and seeded data before test execution.
+- Keep test data isolated per environment (`dev` local, CI database service in workflow).
+
+## Current Gate Stack
+
+- `bun run check`
+- `bun run typecheck`
+- `bun run test`
+- `bun run test:e2e`
+
+## Data Preparation
+
+- `bun run test:e2e:prepare` runs:
+  - Prisma client generation
+  - migration deploy
+  - seed data (including support user bootstrap)
+- `bun run test:e2e` and related scripts call `test:e2e:prepare` automatically.
+
+## Locale Integration Coverage
+
+- `e2e/i18n.pw.ts` covers:
+  - web locale switch + persistence
+  - admin locale switch + persistence
+
+## CI
+
+- Real quality workflow: `.gitea/workflows/ci.yml`
+- Uses a PostgreSQL service container and runs the full gate stack, including e2e.