feat(stack): add revision history comments for force-pushed PRs

When `stack push` force-pushes a PR branch, reviewers have no way to see
what changed between the previous and new commits. This adds a "Revision
History" comment on each updated PR showing all push iterations with:

- Compare links (github.com/owner/repo/compare/old...new) so reviewers
  can see exactly what changed
- Change type labels (content vs rebase) using git patch-id to detect
  whether the force-push changed actual code or just rebased
- Timestamps for each push iteration

The feature is enabled by default. Disable per-push with
`--no-revision-history` or globally with:
  git config --global mergify-cli.stack-revision-history false

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Change-Id: Id77b800246f8ba19cebedb75ca9913a790abcc25

Author: jd

mergify_cli/stack/cli.py

@@ -341,6 +341,15 @@ async def new(
     is_flag=True,
     help="Only update existing pull requests, do not create new ones",
 )
+@click.option(
+    "--no-revision-history",
+    is_flag=True,
+    flag_value=True,
+    default=lambda: not asyncio.run(utils.get_default_revision_history()),
+    help="Don't post revision history comments on pull requests. "
+    "Default fetched from git config if added with "
+    "`git config --add mergify-cli.stack-revision-history false`",
+)
 @utils.run_with_asyncio
 async def push(
     ctx: click.Context,
@@ -356,6 +365,7 @@ async def push(
     trunk: tuple[str, str],
     branch_prefix: str | None,
     only_update_existing_pulls: bool,
+    no_revision_history: bool,
 ) -> None:
     if setup:
         # backward compat
@@ -378,6 +388,7 @@ async def push(
         keep_pull_request_title_and_body=keep_pull_request_title_and_body,
         only_update_existing_pulls=only_update_existing_pulls,
         author=author,
+        revision_history=not no_revision_history,
     )