ci: allow manual trigger of release-please workflow (#365)

## Summary
- Adds `workflow_dispatch` trigger to the release-please workflow so it
can be run manually from the GitHub Actions UI.

## Test plan
- [ ] Verify the "Run workflow" button appears on the Actions page for
this workflow after merge.

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

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Minimal change to CI triggering only; no application logic or release
steps were modified.
> 
> **Overview**
> Adds a manual `workflow_dispatch` trigger to
`.github/workflows/release-please.yml`, allowing Release Please to be
run on-demand from the GitHub Actions UI in addition to running on
`push` to `main`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
e4d5a69. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: Vadman97

.github/workflows/release-please.yml

@@ -3,6 +3,7 @@ name: Run Release Please
 on:
     push:
         branches: [main]
+    workflow_dispatch:
 
 jobs:
     release-package: