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/tsconfig/base.json

@@ -0,0 +1,14 @@
+{
+  "$schema": "https://www.schemastore.org/tsconfig.json",
+  "compilerOptions": {
+    "target": "ESNext",
+    "lib": ["ESNext"],
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "isolatedModules": true,
+    "strict": true,
+    "skipLibCheck": true,
+    "noEmit": true,
+    "types": ["bun"]
+  }
+}

packages/tsconfig/package.json

@@ -0,0 +1,9 @@
+{
+  "name": "@sofa/tsconfig",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "exports": {
+    "./base.json": "./base.json"
+  }
+}