feat: add database-postgres driver boundary package (E00-S03-T02)

- packages/database-postgres (@personal-blog/database-postgres): the single
  workspace package allowed to import the PostgreSQL driver — declares pg and
  kysely as exact dependencies (@types/pg for types) and its src/index.ts
  imports and re-exports the driver pieces (Pool, Kysely, PostgresDialect) so
  the isolation is real, not a placeholder
- pnpm-lock.yaml: importer for packages/database-postgres plus the resolved
  pg/kysely dependency tree (frozen-lockfile install keeps working)
- .gitea/workflows/ci.yml: new database-postgres-imports job runs
  tests/database-postgres-imports.test.mjs on every PR so the isolation
  criterion gates merges

packages/database-postgres/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "@personal-blog/database-postgres",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "description": "EPPP PostgreSQL database adapter package. The single workspace package allowed to import the pg driver and Kysely (E00-S03-T02); the concrete adapter (migration ledger, advisory lock) lands in later stories.",
+  "scripts": {
+    "build": "tsc -p tsconfig.json",
+    "typecheck": "tsc -p tsconfig.json --noEmit"
+  },
+  "dependencies": {
+    "kysely": "0.29.5",
+    "pg": "8.23.0"
+  },
+  "devDependencies": {
+    "@types/pg": "8.23.1"
+  },
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js"
+    }
+  }
+}