Add copy and open-in-editor options to the command log menu

[tmwatchanan]

PR Description

Git hook and push output is easy to read in lazygit's command log but difficult to copy, especially when the output spans multiple lines. Terminal selection is awkward and often picks up neighbouring panels. Related discussion: #3031, including this suggestion to open log output in $EDITOR.

This adds three entries to the command log menu (@):

1. Copy last git output to clipboard (c)
2. Copy all git outputs to clipboard (a)
3. Open command log in editor (o) — writes the full log to a temp file and opens it in the configured editor.

Copy items include the lazygit action, the indented git command(s) above the block, and everything under Git output:. The editor export uses the same underlying log content, without panel chrome or copy-notification lines.

Implementation notes:

• Parses git output blocks from the command log view buffer; copy boundaries respect real stderr (indented stack traces, multi-line tool errors) rather than treating every two-space line as log noise.
• Uses CopyToClipboardQuiet so writing to the clipboard is not logged back into the command log stream.
• Menu items re-evaluate disabled state while the menu is open (e.g. copy/open stay disabled until there is output).
• Exposes LastGitOutput() and AllGitOutput() on IGuiCommon for custom commands.

Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc