fix(installer): strip stale auto-sync hooks on install and uninstall (#278)

Pre-0.8 installers wrote `codegraph mark-dirty` / `sync-if-dirty` hooks
to Claude Code's settings.json. Both subcommands were removed from the
CLI, so the Stop hook fails every turn ("unknown command
'sync-if-dirty'"). The cleanup that once removed them was lost when the
installer moved to the per-target architecture.

Add cleanupLegacyHooks(), wired into both install (upgrades self-heal)
and uninstall (so the npm preuninstall step fully reverses a legacy
install). Surgical at the command level: only codegraph's own hook
entries are dropped, so unrelated hooks sharing a matcher group or event
(e.g. GitKraken's `gk ai hook run`) survive, and a settings.json with no
legacy hooks is left byte-for-byte untouched.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -21,6 +21,20 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   signatures, generics, and Roblox instance-path `require(script.Parent.X)`
   imports.
 
+### Fixed
+- **Installer**: re-running `codegraph install` now removes the broken
+  auto-sync hooks that pre-0.8 versions wrote to Claude Code's
+  `settings.json`. Those builds added a `Stop → codegraph sync-if-dirty`
+  hook (and a `PostToolUse → codegraph mark-dirty` partner); both
+  subcommands were later removed from the CLI, so Claude Code reported
+  `Stop hook error: ... unknown command 'sync-if-dirty'` on every turn.
+  The cleanup is surgical — only codegraph's own hook entries are
+  stripped, so unrelated hooks sharing the same file or event (e.g. a
+  GitKraken `gk ai hook run` hook) are left untouched — and it also runs
+  on uninstall, so the npm `preuninstall` step fully reverses a legacy
+  install. Re-run `codegraph install` once on an affected machine to
+  clear the error.
+
 ## [0.8.0] - 2026-05-20
 
 ### Added