fix: remove hardcoded localhost default arg from GET /api/keys, unify coverage to single coverage/ dir, fix test to pass explicit Request

- Remove `new Request('http://localhost/api/keys')` default arg from GET handler in src/app/api/keys/route.ts (line 26)
- Fix api-key-reveal-route.test.mjs to pass explicit Request instead of calling GET() with no args
- Add --output-dir coverage to all c8 scripts in package.json
- Add coverage.reportsDirectory: 'coverage' to vitest.config.ts and vitest.mcp.config.ts
- Fix CHANGELOG.md structure (# Changelog + [Unreleased] to top)
- Remove 30+ stale coverage-* directories from project root
- Coverage: Statements 78.76% | Branches 72.75% | Functions 80.93% | Lines 78.76% (all thresholds passed)

next.config.mjs

@@ -1,9 +1,11 @@
 import createNextIntlPlugin from "next-intl/plugin";
 
 const withNextIntl = createNextIntlPlugin("./src/i18n/request.ts");
+const distDir = process.env.NEXT_DIST_DIR || ".next";
 
 /** @type {import('next').NextConfig} */
 const nextConfig = {
+  distDir,
   // Turbopack config: redirect native modules to stubs at build time
   turbopack: {
     resolveAlias: {