test(pi): sandbox review-server tests from the user's config (#1624)

apps/pi-extension/server.test.ts and packages/server/review-workspace.test.ts
boot real review servers that read config.json from the data dir. The root
bunfig preload points PLANNOTATOR_DATA_DIR at a temp dir, but bun only loads
it from the repo root; run from the package directory (apps/pi-extension's
own `bun test` script, or `bun test` inside packages/server) the tests read
the contributor's real ~/.plannotator/config.json. With
reviewAnalysis.semanticDiff: false there, 6 tests fail in each file.

Point PLANNOTATOR_DATA_DIR at a fresh temp dir in a beforeEach; the existing
afterEach already restores it.