Add windows support

[tommyjcarpenter]

Add windows support

Cross-platform additions

• auto-detect systype from sys.platform (mac/arch/ubuntu/windows)
• replace shell mkdir -p / ln -f -n -s with os.makedirs / os.symlink
  (target_is_directory matters on Windows where file/dir symlinks differ)
• HOMEDIR via os.path.expanduser("~") so Windows works without $HOME

Windows package managers

• winget package type with winget list precheck (skips already-installed
  packages whose "upgrade" exits non-zero with no available newer version)
• scoop and scoop_bucket package types
• scoop installs run one at a time with shortcircuit=False so a single missing
  manifest doesn't abort the rest of the batch (matches winget behavior)
• npm on Windows skips sudo (user-writable global prefix; no sudo on Windows)
• _refresh_windows_path() re-reads HKLM+HKCU PATH after each _run_cmd, and
  before each _run_check, so prechecks see packages installed in prior runs
  even when the parent shell's environment is stale

New pip package type

• python3 -m pip install --user on POSIX (system-Python protections)
• python -m pip install on Windows (winget Python's Scripts dir is on PATH;
  the --user Scripts dir is not, which would leave installs invisible)

New file_associations config section (Windows)

• per-user registration under HKCU\Software\Classes (no admin needed)
• writes ext -> ProgID, ProgID name (FriendlyAppName), DefaultIcon, and
  shell\open\command — chosen so the "Open with" picker shows a real app
  name instead of the launcher exe metadata or "Shim"
• preserves UserChoice if it already points to our ProgID; only clears it
  when it points elsewhere, so a user's "Always use this app" selection
  survives subsequent bootstrap runs

Misc

• schema updated for windows section and file_associations
• README documents new package types and the file_associations section
• sample_config.json rewritten to current schema with windows + new features
• drop dead _gitclone() helper (never called, not part of the schema)
• bump to 1.4.0