Adds 'aisurface doctor' (install-health self-check, 7 checks) and
'@safe_dispatch' wrapper (catches 4 user-facing exception classes) so
Windows users get actionable hints instead of stack traces when the
console script isn't on PATH.

- 4th subcommand: doctor (Python version, scripts importable, console
  script on PATH, deps, cache writable, PyPI latest, PERPLEXITY_API_KEY)
- @safe_dispatch: ModuleNotFoundError / FileNotFoundError /
  UnicodeEncodeError / PermissionError on cache -> actionable stderr hint
- README 5-min self-test: uses 'python -m scripts.cli' (cross-platform)
- CI: 15-job matrix (3 OS x 5 Python 3.10-3.14) with doctor smoke test
- 140 tests pass (128 non-eval + 12 eval), ruff clean

Fixes the v1.0.1 README 5-min self-test failure on Windows where the
aisurface console script lives in %APPDATA%\Python\Python3X\Scriptswhich is not on PATH by default.