fix(mitm): generate root ca on server startup

[Jordannst]

Description

Fixes #2224.

Direct MITM server startup could fail before the Root CA was ever created because server.js read rootCA.key / rootCA.crt immediately and exited when either file was missing. That bypasses the manager.js setup path that normally generates the CA.

Changes

• Generate the MITM Root CA from server.js when rootCA.key or rootCA.crt is missing.
• Make generateRootCA() / generateCert() synchronous, matching their filesystem work and avoiding a startup race before readFileSync.
• Add a targeted unit test proving Root CA files are created synchronously for direct server startup.

Verification

./node_modules/.bin/vitest run tests/unit/mitm-root-ca.test.js
node --check src/mitm/server.js && node --check src/mitm/cert/rootCA.js && node --check src/mitm/cert/generate.js
git diff --check

Also ran:

./node_modules/.bin/vitest run tests/unit/mitm-root-ca.test.js tests/unit/antigravity-mitm.test.js

The new MITM Root CA test passed. tests/unit/antigravity-mitm.test.js has an unrelated existing failure on the out-of-box Antigravity mandatory model assertion (expected undefined to be true).