Paka 0.15.0 capture preview 3.3

Point release on top of capture preview 3.2: a small rendering refinement, with no change to app behavior beyond sharper code layout.

• Rendered barcodes and QR codes now snap to an exact whole-module pixel grid, so every module is an identical width with no leftover quiet-zone pixels and no sub-pixel draw drift
• Raised the internal render cap so a future enlarged/zoom code view can be drawn at native resolution instead of upscaling
• Payload verification is unchanged; every rendered code is still decoded and checked against its source before display
• Added a security policy and security-contact metadata (SECURITY.md, .well-known/security.txt), a threat model, and a persistence/backup format registry under docs/
• Added a device-testing checklist, a release checklist, and a security/longevity roadmap
• CI now guards APK permissions on the debug, preview, and unsigned release builds, failing if internet, network-state, or any unexpected permission ever appears in the merged manifest
• Added tools/verify_release_apk.sh and tools/check_apk_permissions.sh for local certificate and permission verification
• Corrected the photo format registry to list every supported image header (JPEG, PNG, GIF, WebP, HEIF/HEIC, AVIF) and hardened the verification scripts (aapt2 fallback, version-ordered build-tools selection)

At normal panel size codes already rendered on an integer grid, so this is a subtle cleanup rather than a visible change; the extra headroom matters mainly for a later enlarge/fullscreen view.

Signed like the regular releases, so it installs as an update over an existing Paka installation (including earlier previews). Source is on the preview/document-capture branch; main remains at 0.14.0.