fix(hooks): make Windows hooks work + self-heal stale settings entries

[BernardMasika]

fix(hooks): make Windows hooks work, and self-heal stale settings entries

What was happening

On Windows, every prompt was blocked with:

UserPromptSubmit operation blocked by hook:
[if (Get-Command node -ErrorAction SilentlyContinue) { node "...fableit-mode-tracker.js" }]:
/usr/bin/bash: -c: line 1: syntax error near unexpected token `{'

Claude Code runs hook commands through bash on every platform (Git Bash on
Windows), but the commandWindows fields were written in PowerShell
(if (...) { }, Get-Command -ErrorAction). Bash can't parse that, and because
those variants had no trailing ; exit 0, the non-zero exit caused the
UserPromptSubmit hook to block the prompt on every submission.

This bit users through two paths:

1. Marketplace-plugin install reads hooks/hooks.json directly.
2. npx fableit install derives a hooks block into ~/.claude/settings.json
   via bin/fableit.js, and on Windows it copied the PowerShell commandWindows
   value in verbatim. This is the copy that actually fired for affected users,
   which is why fixing only hooks.json didn't unblock an existing install.

Changes

hooks/hooks.json — remove the PowerShell commandWindows variants. The
plain command field is already correct and cross-platform: forward slashes
work with node on Windows, and ; exit 0 guarantees a hook never blocks a
prompt. No behaviour change on macOS/Linux.

bin/fableit.js

• hookEntries() no longer emits the PowerShell variant into settings.json.
  It substitutes the plugin-root placeholder and normalises to forward slashes,
  so the written command is valid bash on Windows too.
• installClaude() now reconciles instead of appends. Re-running install
  drops any previous fableit entry (including a stale or broken PowerShell one
  from an older version) and re-adds the current correct one. Users self-heal on
  the next update instead of hand-editing settings.json. It's idempotent and
  leaves the user's own unrelated hooks untouched.
• isOurs now compares with separators normalised, so an entry written with
  either slash style is recognised (the old backslash-only marker would miss a
  bash command). CLI dispatch is guarded with require.main and the helpers are
  exported so they can be unit-tested.

Tests + CI (so this can't regress)

Run under the existing npm test (node --test), on ubuntu-latest and
windows-latest in CI, since the bug was Windows-specific.

• tests/hooks.test.js: hooks.json is valid JSON with the right shape; every
  shell-bearing field (command and any legacy commandWindows) parses under
  bash -n (the exact check that catches PowerShell syntax); referenced scripts
  exist; the hook scripts always exit 0 on real, ordinary, empty, and garbage
  stdin. A known-bad fixture is asserted to be rejected, so the guard can't
  silently pass everything.
• tests/installer.test.js: reconcile replaces a stale PowerShell entry with a
  valid bash one, preserves the user's own hooks, is idempotent, and every
  command the installer emits is valid bash.

Verification

$ npm test
# tests 14
# pass 14
# fail 0

Swapping the pre-fix hooks.json back in fails the suite with a message
pointing straight at the offending commandWindows field.

Note for existing (already-broken) installs

With reconcile in place, affected users are fixed automatically the next time
npx fableit runs (e.g. on update). No manual settings.json editing needed.