tests: consolidate into tests/ dirs, fix import paths

Move all test files out of source dirs into per-workspace tests/:
- shared/tests/   (3 unit test files)
- server/tests/   (1 integration test)
- src/tests/      (8 characterization + scenario tests + testHelpers)

Fix all relative import paths (App, storage, __mocks__, testHelpers).
Fix jest.config testMatch globs in shared/ and server/ (rootDir +
<rootDir>/tests pattern).

Delete scripts/repro-pause-bug.js (debug scratch, superseded by
turn.pause-add.test.js).

Keep scripts/replay-combat.js + scripts/audit-rotation.js as manual
demo/exploratory tools (NOT unit tests, not deterministic).

No logic changes. All green: shared 49 + 1 validated RED, server 23,
FE 62. Scenario test unchanged (240s timeout, pre-existing slow).

shared/jest.config.js

@@ -1,5 +1,6 @@
 module.exports = {
+  rootDir: '.',
   testEnvironment: 'node',
-  testMatch: ['**/*.test.js'],
+  testMatch: ['<rootDir>/tests/**/*.test.js'],
   collectCoverageFrom: ['turn.js'],
 };