chore: extract shared tsconfig, move display-status to core, add i18n tests

- Add `@sofa/tsconfig` package with a shared `base.json` (target, lib, strict, moduleResolution, etc.) and migrate all packages/apps to `"extends": "@sofa/tsconfig/base.json"` to eliminate duplicated compiler options
- Move `display-status.ts` (and its `DisplayStatus` type + `getDisplayStatus` fn) from `@sofa/api` to `@sofa/core`; remove the `./display-status` export from `@sofa/api` and update all import sites in `discovery.ts` and `tracking.ts`
- Add `packages/core/test/display-status.test.ts`: 15 tests covering `ONGOING_TMDB_STATUSES` and all `getDisplayStatus` branches (movie, TV watchlist/in_progress/caught_up/completed, edge cases)
- Add `packages/i18n/vitest.config.ts` and two new test files: `date-buckets.test.ts` and `format.test.ts` covering date bucketing and locale formatting utilities

packages/api/package.json

@@ -7,8 +7,7 @@
     "./contract": "./src/contract.ts",
     "./schemas": "./src/schemas.ts",
     "./errors": "./src/errors.ts",
-    "./utils": "./src/utils.ts",
-    "./display-status": "./src/display-status.ts"
+    "./utils": "./src/utils.ts"
   },
   "scripts": {
     "lint": "oxlint",
@@ -21,6 +20,7 @@
     "zod": "catalog:"
   },
   "devDependencies": {
+    "@sofa/tsconfig": "workspace:*",
     "typescript": "catalog:"
   }
 }