fix(tools): classify git bisect as a worktree mutation

bisect sat in _KNOWN_GIT_BUILTINS and was allowed in the running source
root, yet it repeatedly checks out commits — the exact module-version
skew this guard exists to prevent. Move it to _WORKTREE_MUTATIONS.

tests/tools/test_self_repo_guard.py

@@ -30,6 +30,8 @@ class TestBlocksMutationsInSourceRepo:
         [
             "checkout pr-51020",
             "switch main",
+            "bisect start",
+            "bisect good HEAD~10",
             "reset --hard origin/main",
             "reset --har origin/main",
             "rebase origin/main",

tools/self_repo_guard.py

@@ -27,6 +27,9 @@ _WORKTREE_MUTATIONS = frozenset({
     "clean",
     "cherry-pick",
     "revert",
+    # bisect drives repeated checkouts of the running root — the exact
+    # module-version-skew hazard this guard exists for.
+    "bisect",
 })
 _WORKTREE_TARGET_ACTIONS = frozenset({"move", "remove"})
 _STASH_SAFE_ACTIONS = frozenset({"list", "show", "create", "store", "drop", "clear"})
@@ -35,7 +38,6 @@ _KNOWN_GIT_BUILTINS = frozenset({
     "add",
     "am",
     "apply",
-    "bisect",
     "blame",
     "branch",
     "bundle",