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/update.go

@@ -155,15 +155,3 @@ func (m *Model) handleInstalled(msg installedMsg) {
 	m.updated = msg.release.Tag
 	m.flash = done("updated to lazysecrets " + msg.release.Tag + " · restart lazysecrets to use it")
 }
-
-// updateLabel is the version's suffix in the footer: a newer release to
-// update to, or the one installed and waiting for a restart.
-func (m Model) updateLabel() string {
-	switch {
-	case m.updated != "":
-		return " → " + m.updated + " (restart)"
-	case m.newer != nil:
-		return " ↑ " + m.newer.Tag + withKey(m.keys.Update, " %s")
-	}
-	return ""
-}