feat(git): 3-way merge editor, reflog, rebase/interactive rebase, reset with undo, force-with-lease push, remote branches and remotes

Server: git-rewrite.js (rebase + continue/skip/abort, rebase-interactive with
no editor, reset soft/mixed/keep/hard, undo-rewrite, force-push with lease,
remote-branch-delete, remote add/rename/remove) and git-conflicts.js
(conflict stages read + conflict-save, reflog), dispatched from runGitAction;
operationInProgress now reports a rebase and only ALLOWED_WHILE_REBASING
writes run during one. New reads: /git/conflict, /git/reflog, /git/remotes,
/git/rewrite-plan. Client: History tools menu, MergeEditor, ReflogView,
RebaseDialog, InteractiveRebase, ResetDialog, ForcePushDialog, RemotesDialog,
rebase banner Skip. CLAUDE.md git-writes rule rewritten for the new actions.

server/__tests__/git-diff-ops.test.js

@@ -291,7 +291,7 @@ describe("runGitAction", () => {
   beforeEach(freshFixture);
 
   it("rejects an unknown action", async () => {
-    await assert.rejects(() => runGitAction(LANE, "rebase"), { code: "EBADACTION" });
+    await assert.rejects(() => runGitAction(LANE, "frobnicate"), { code: "EBADACTION" });
   });
 
   it("commits everything with the given message", async () => {