feat: link each changelog entry to its PR and commit (#11)

Like Immich's and RomM's release notes: every changelog entry now links to its pull request and its commit, in `CHANGELOG.md` and in the release notes on Gitea:

```
- Search with fzf's scoring and query syntax ([#11](…/pulls/11)) ([65dc2d7](…/commit/65dc2d7…))
```

- `cliff.toml`: the entry template adds the short commit hash as a link; a postprocessor turns the squash commit's `(#N)` into a link to the PR.
- The app shows release notes as text (`U`, and the status pane's changelog to come), so `Release.Notes()` turns Markdown links back into their text: `Search (#11) (65dc2d7)`.

Checked with `git cliff --unreleased` on main: every entry since v0.1.0 gets both links. Test for the link stripping.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>
Reviewed-on: #11

internal/ui/app/commands.go

@@ -53,6 +53,9 @@ func paneContext(p pane) string {
 
 // commandsHere are the custom commands for the focused pane.
 func (m *Model) commandsHere() []commands.Command {
+	if m.focus == paneStatus {
+		return nil
+	}
 	var out []commands.Command
 	for _, c := range m.commands {
 		if c.Context == commands.Global || c.Context == paneContext(m.focus) {