Show relative commit age in the compact commits view

### Is your feature request related to a problem? Please describe

I usually keep the commits panel in normal/compact screen mode. It shows the
commit hash, author, graph, and subject, but not when each commit was created.

The timestamp becomes visible after enlarging the panel with `+`, but this
changes the layout and shows an absolute date or time. I would like to see the
relative age while keeping the compact one-line layout, especially when
scanning recent commits.

### Describe the solution you'd like

Add an optional relative-age column to commit rows in the compact view:

82c03593 4m IL ○─ Merge pull request...
059c9ca0 2h IL ○ Leave the pause...
ece5ac1a 3d IL ○ Merge pull request...

Using the same short representation as the branches panel (`4m`, `2h`, `3d`)
would keep the column narrow and make the two panels consistent.

This could be exposed as either:

- a toggle in the commits Log menu, with the choice persisted; or
- an opt-in configuration setting such as `showCommitAgeInCompactView`.

The existing compact layout should remain the default.

### Current implementation

The required data and formatter already appear to exist:

- Commits contain `UnixTimestamp`.
- `utils.UnixToTimeAgo(timestamp)` in `pkg/utils/date.go` converts a Unix
timestamp into the compact `s`, `m`, `h`, `d`, `w`, `M`, or `y` format.
- `pkg/commands/git_commands/branch_loader.go` uses `UnixToTimeAgo` when
populating `Branch.Recency`, which is rendered as the first column in the
branches panel.
- Stash entries use the same formatter.
- In `pkg/gui/presentation/commits.go`, `displayCommit` already has access to
`commit.UnixTimestamp`. However, its date column is populated only when
`fullDescription` is true:

descriptionString := ""
if fullDescription {
descriptionString = style.FgBlue.Sprint(
utils.UnixToDateSmart(
now,
commit.UnixTimestamp,
timeFormat,
shortTimeFormat,
),
)
}

- `fullDescription` is passed by the commits context when the screen mode is
not `SCREEN_NORMAL`, which explains why the timestamp appears after pressing
`+` but not in the normal compact view.

A possible implementation would therefore reuse `UnixToTimeAgo` for the
description column when compact relative ages are enabled, without requiring
another Git command or additional commit data.

Relevant files:

- `pkg/utils/date.go`
- `pkg/commands/git_commands/branch_loader.go`
- `pkg/gui/presentation/branches.go`
- `pkg/gui/presentation/commits.go`
- `pkg/gui/context/local_commits_context.go`

### Describe alternatives you've considered

- Enlarging the commits panel with `+`. This shows a timestamp, but changes the
layout and uses `timeFormat` / `shortTimeFormat` rather than relative age.
- Customizing `branchLogCmd`. It can display `%cr`, but only changes the branch
log in the main panel and does not affect the interactive commits list.
- Opening a separate `git log` or `tig` view. This loses the integrated lazygit
commit workflow.

### Additional context

PR #5846 proposes `normal`, `comfortable`, and `spacious` commit display
formats, with author and date on a second line in the latter two modes:

https://github.com/jesseduffield/lazygit/pull/5846

That proposal is related, but this request is specifically about showing a
small relative-age column in the existing one-line compact layout.

Start in pkg/gui/presentation/commits.go and inspect displayCommit and the fullDescription path, then compare the relative-age handling in pkg/commands/git_commands/branch_loader.go and pkg/gui/presentation/branches.go. Review pkg/gui/context/local_commits_context.go for the compact-view configuration or menu path. Done means an opt-in relative-age column appears in compact commit rows, while the existing compact layout remains the default.

Written by the indexing model from the issue text.