ci: drop Windows runner, add static hardcoded-path detection (#1676)

Replace the Windows CI runner with a static analysis test that catches
the same class of platform-specific path bugs (C:\, /home/, /Users/,
/tmp/) without requiring an actual Windows machine.

- tests/hardcoded-paths.test.cjs: new static scanner that checks string
  literals in all source JS/CJS files for hardcoded platform paths;
  runs on Linux/macOS in <100ms and fires on every PR
- .github/workflows/test.yml: remove windows-latest from matrix; switch
  macOS smoke-test runner from Node 22 → Node 24 (the declared standard)
- package.json: bump engines.node from >=20.0.0 to >=22.0.0 (Node 20
  reached EOL April 2026)

Matrix goes from 4 runners → 3 runners per run:
  ubuntu/22  ubuntu/24  macos/24

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/test.yml

@@ -24,12 +24,12 @@ jobs:
         os: [ubuntu-latest]
         node-version: [22, 24]
         include:
-          # Single macOS runner — verifies platform compatibility
+          # Single macOS runner — verifies platform compatibility on the standard version
           - os: macos-latest
-            node-version: 22
-          # Single Windows runner — slowest CI runner, smoke-test only
-          - os: windows-latest
-            node-version: 22
+            node-version: 24
+          # Windows path/separator coverage is handled by hardcoded-paths.test.cjs
+          # and windows-robustness.test.cjs (static analysis, runs on all platforms).
+          # A dedicated windows-compat workflow runs on a weekly schedule.
 
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2