fix(sync): filesystem-based change detection (catch git pull & non-git edits) (#414)

* fix(sync): detect changes via filesystem, not git status

Incremental sync detected changes with `git status --porcelain`, which only sees uncommitted working-tree changes — so committed changes from git pull/checkout/merge/rebase (clean tree afterward) were never reconciled, and non-git projects leaned on a slow full rescan. Change detection is now filesystem-based and git-independent: a (size, mtime) stat pre-filter skips unchanged files, then a content hash confirms the rest; removals are checked against the filesystem (git ls-files still lists deleted-but-unstaged files). Also adds a non-blocking catch-up sync on MCP connect so changes made while the server was down (e.g. a terminal git pull) are reconciled on connect.

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

* docs(changelog): add 0.9.5 entry for filesystem-based sync fix

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

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