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/panes/fields.go

@@ -19,10 +19,13 @@ type Fields struct {
 }
 
 // Field is a row: a value under a label. Info rows (loading, errors)
-// can't be copied; Err ones are errors.
+// can't be copied; Err ones are errors. A row can also be opened: URL in
+// the browser (o), Path in the editor (e), or Provider signed in to (L).
 type Field struct {
 	Label, Value string
 	Info, Err    bool
+
+	URL, Path, Provider string
 }
 
 func NewFields() Fields {