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/testdata/TestGolden.golden

@@ -1,8 +1,11 @@
-╭─ [1] Sources - Favourites ────╮╭─ platform-prod ─────────────────────────────────────────────────╮
-│ ▾ Azure (2)                   ││ name       platform-prod                                        │
-│   platform-prod               ││ ID         sub-prod                                             │
-│   platform-dev                ││ web        https://portal.azure.com/#resource/subscriptions/sub…│
-│ ▾ Databricks (2)              ││ vaults     3                                                    │
+╭─ [0] lazysecrets ─────────────╮╭─ platform-prod ─────────────────────────────────────────────────╮
+│ 2 accounts                    ││ name       platform-prod                                        │
+╰───────────────────────────────╯│ ID         sub-prod                                             │
+╭─ [1] Sources - Favourites ────╮│ web        https://portal.azure.com/#resource/subscriptions/sub…│
+│ ▾ Azure (2)                   ││ vaults     3                                                    │
+│   platform-prod               ││                                                                 │
+│   platform-dev                ││                                                                 │
+│ ▾ Databricks (2)              ││                                                                 │
 │   prod                        ││                                                                 │
 ╰────────────────────── 2 of 6 ─╯│                                                                 │
 ╭─ [2] Vaults ──────────────────╮│                                                                 │