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/workflows/nightly-release.yml

@@ -0,0 +1,35 @@
+name: Nightly Release
+
+on:
+  push:
+    branches: [main, master]
+  workflow_dispatch:
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  nightly-build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Set version
+        id: version
+        run: |
+          DATE=$(date -u +%Y%m%d%H%M)
+          SHA=$(git rev-parse --short HEAD)
+          VERSION=$(grep -m1 '^version =' Cargo.toml | cut -d'"' -f2)
+          echo "VERSION=${VERSION}-nightly.$DATE.$SHA" >> $GITHUB_OUTPUT
+
+      - name: Create nightly release
+        uses: softprops/action-gh-release@v3
+        with:
+          tag_name: nightly-${{ steps.version.outputs.VERSION }}
+          name: Nightly Build ${{ steps.version.outputs.VERSION }}
+          prerelease: true
+          generate_release_notes: true