feat(platform): Add Windows support for session storage paths

[sunilp]

Summary

Ensure session/history storage paths work correctly on Windows.

Current State

src/storage/history.ts handles macOS (~/Library/Application Support/jam/) and Linux (~/.local/share/jam/) with a Windows fallback to %APPDATA%/jam/, but this path handling needs testing and may need adjustments.

Tasks

• Verify getSessionDir() works correctly on Windows
• Ensure path separators are handled correctly (path.join should handle this)
• Test that ensureDir() creates directories correctly on Windows
• Add unit tests with mocked process.platform values
• Test with actual Windows environment if possible
• Update README if any Windows-specific notes are needed

Files

• src/storage/history.ts — getSessionDir() function
• src/storage/history.test.ts — add platform-specific tests

Acceptance Criteria

• Session storage works on Windows
• Tests cover all three platforms (macOS, Linux, Windows)
• No regressions on macOS/Linux

[sunilp]

✅ Implemented and verified — closing

Merged in #11 (commit 1c908d9).

Delivered (additions to src/storage/history.test.ts):
5 platform-specific tests covering all required platforms:

• macOS (darwin) — uses ~/Library/Application Support/jam/sessions/
• Linux + XDG_DATA_HOME set — uses $XDG_DATA_HOME/jam/sessions/
• Linux + XDG_DATA_HOME unset — falls back to ~/.local/share/jam/sessions/
• Windows (win32) + APPDATA set — uses %APPDATA%/jam/sessions/
• Windows (win32) + APPDATA unset — falls back to homedir

Each test mocks process.platform and the relevant env vars, then verifies that createSession / getSession / listSessions work end-to-end.

Test results — 18/18 history tests pass (npm test, 160 total):

✓ src/storage/history.test.ts (18)
  history storage (13 tests)
  getSessionDir() platform paths (5 tests)
    uses     uses     uses     uses     uses     uses     uses     uses     uses     uses     uses     uses     uses     uses     uses     usesXDG    uses     uses     uses     usATA     uses     uses     uses     uses     uses     uses  n Windows when APPDATA is unset