Force squash across merges: UI dialog, safety toggle, and env support

[denis-kudelin]

• Adds “Force squash to here…” in the commit context menu, gated by Preferences → “Enable dangerous history rewrites.”
• New dialog with options: create backup branch, auto-stash local changes, keep target commit’s author/date, append messages from squashed commits.
• Implementation: soft-reset to the target’s first parent, create a single commit, restore stash, then open Push dialog with Force Push preselected.
• Adds new commands: IsAncestor, DiffAll, DiffStat; extends Command with Envs to pass env vars (e.g., GIT_COMMITTER_DATE).
• Updates localizations for all supported languages.

[love-linger]

I'm very sorry, but I don't want this operation to be introduced into SourceGit. As shown in your code, this is a combined command. Users can originally complete this operation in the following steps:

Step 1. Stash local changes. (Optional)
Step 2. Create a temp branch based the merge source branch or just checkout it. (Optional. If they do NOT want to backup original branch, they can use it directly)
Step 3. Interactive-Rebase source branch (checkouted on Step 2) to target branch

[denis-kudelin]

I'm very sorry, but I don't want this operation to be introduced into SourceGit. As shown in your code, this is a combined command. Users can originally complete this operation in the following steps:

Step 1. Stash local changes. (Optional) Step 2. Create a temp branch based the merge source branch or just checkout it. (Optional. If they do NOT want to backup original branch, they can use it directly) Step 3. Interactive-Rebase source branch (checkouted on Step 2) to target branch

I know it’s dangerous, but I work with a large number of repositories and I’m tired of cleaning up history. By the way, I hid this feature behind a checkbox in the settings. Nobody will click it by accident.