Add OpenWhispr easy setup installer and companion files

Single-file bash installer (setup-openwhispr.sh) with distro detection,
dependency installation, STT/AI cleanup provider selection, API key
management, and first-run launch. Includes README, LICENSE (MIT),
CHANGELOG, .gitignore, ShellCheck CI, issue templates, PR template,
and GitHub setup guide.

https://claude.ai/code/session_01XKYC1basxdwtHy71tky7xm

.github/pull_request_template.md

@@ -0,0 +1,19 @@
+## What does this PR do?
+
+Brief description of the change.
+
+## Checklist
+
+- [ ] `bash -n setup-openwhispr.sh` passes (no syntax errors)
+- [ ] ShellCheck passes with no new warnings
+- [ ] Tested on at least one supported distro
+- [ ] Updated CHANGELOG.md if user-facing
+- [ ] No hardcoded paths or usernames (uses YOUR_USERNAME placeholder or is generic)
+
+## Testing
+
+Describe how you tested this change.
+
+## Related issues
+
+Closes #