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/labeler.yml

@@ -4,7 +4,7 @@ documentation:
 
 features:
   - changed-files:
-      - any-glob-to-any-file: ['src/input.rs', 'src/lock.rs', 'src/config.rs']
+      - any-glob-to-any-file: ['src/input.rs', 'src/lock.rs', 'src/config.rs', 'src/auth.rs', 'src/screenshot.rs', 'src/system.rs']
 
 rendering:
   - changed-files:
@@ -20,4 +20,4 @@ dependencies:
 
 refactoring:
   - changed-files:
-      - any-glob-to-any-file: ['src/util.rs', 'src/system.rs', 'src/main.rs']
+      - any-glob-to-any-file: ['src/util.rs', 'src/main.rs']