feat: ring shapes, auth reuse, input tests, README docs, CI improvements

- Add --ring-shape (circle/square/diamond/hexagon/pill) with geometry module
- Reuse PAM context across auth attempts (no reload per-keystroke)
- Proper error propagation in screenshot effects (unwrap → Result + context)
- Remove theme presets (modern/pixel/glass) and --theme flag
- Add input cooldown after failed attempt (400ms debounce)
- Add Ctrl+held peek password, Home/End/Delete cursor keys
- Add all input unit tests (23 new tests)
- Add --max-dots, feedback duration, timeout, interval config options
- Add --log-path, --auth-timeout, verifying_color config fields
- Remove unused deps: futures, gio, env_logger, num-traits, thiserror, bytemuck
- Fix media bar: remove stop button, fix art+text overlap, uniform hit areas
- Fix CI: source-only releases, nightly prereleases, dependabot groups, labeler paths
- Update issue templates with structured forms
- Add stale workflow for inactive issues/PRs
- Update README: full options table (28 flags), remove theme docs, add shapes

.github/ISSUE_TEMPLATE/feature_request.md

@@ -1,4 +1,8 @@
-# Feature Request
+---
+name: Feature Request
+about: Suggest an idea for rustlock
+labels: enhancement
+---
 
 **Is your feature request related to a problem? Please describe.**
 
@@ -9,4 +13,4 @@
 **Describe alternatives you've considered**
 
 
-**Additional context**
+**Additional context**