fix: exclude test files from tsc build to unbreak Docker CI

tsconfig included src/**/__tests__/** and *.test.ts, so `npx tsc` in
Dockerfile compiled test files. When test fixtures drifted from changed
interfaces (e.g. CurlFetchResponse gaining/losing fields), Docker build
failed even though Vitest passed. Exclude test globs from the build
tsconfig and fix the stale `headers` property in update-checker mocks.

src/__tests__/update-checker.test.ts

@@ -68,7 +68,6 @@ describe("update-checker writes to data/, not config/", () => {
       ok: true,
       status: 200,
       body: APPCAST_XML,
-      headers: {},
     });
 
     // Dynamic import to get fresh module state
@@ -97,7 +96,6 @@ describe("update-checker writes to data/, not config/", () => {
       ok: true,
       status: 200,
       body: APPCAST_XML,
-      headers: {},
     });
 
     const { checkForUpdate } = await import("../update-checker.js");
@@ -115,7 +113,6 @@ describe("update-checker writes to data/, not config/", () => {
       ok: true,
       status: 200,
       body: APPCAST_XML,
-      headers: {},
     });
 
     const { checkForUpdate } = await import("../update-checker.js");

tsconfig.json

@@ -15,5 +15,5 @@
     "isolatedModules": true
   },
   "include": ["src/**/*.ts"],
-  "exclude": ["node_modules", "dist"]
+  "exclude": ["node_modules", "dist", "src/**/__tests__/**", "src/**/*.test.ts"]
 }