Add restore deleted branches and their upstreams

[borngraced]

PR Description

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Adds two related capabilities for recovering branches that no longer show up in the branch list:

1. Restore deleted local branches: Branches deleted in lazygit are now detected via the reflog and listed in the branch panel with a "deleted branch" badge. A new keybinding (<ctrl+r> in the branches panel) opens a menu to recreate the selected deleted branch at its last commit. If exactly one matching remote-tracking ref survives, the upstream is re-attached automatically.
2. Restore deleted remote branches: When a branch's remote was deleted (e.g. on GitHub) and the local branch shows "(upstream gone)", a new "Restore upstream branch" item in the upstream options menu (u → p) pushes the local branch back to its configured remote, recreating the branch and clearing the gone state.

Includes unit tests for deleted-branch detection (with hardening against reflog noise like SHA-like refs and orphaned checkout entries) plus integration tests covering both the delete-and-restore flow and the upstream-gone restore.