Add Snacks app: automated video library encoder with hardware acceleration (#6)

Co-authored-by: Joachim Friberg <joachim.friberg@ip-solutions.se>
Reviewed-on: phirna/zima-apps#6

apps.md

@@ -0,0 +1,15 @@
+## Backlog
+
+| # | Done | Name | Source | What | Agent instructions |
+|---|---|---|---|---|---|
+| 1 | [x] | Snacks | https://github.com/derekshreds/snacks | Automated video library encoder | Branch `snacks/initial/add-video-encoder`; implemented in `Apps/snacks/` |
+
+## Adding a new app
+
+1. Copy `Apps/_template/` → `Apps/<app-id>/`
+2. Set `name` in compose (lowercase + hyphen only)
+3. Pin image to explicit version/tag (no `:latest`); verify tag exists in registry
+4. Add `x-casaos` metadata (title, description, icon, category, author, port_map)
+5. Write `README.md` with purpose, ports, volumes, envs, and risk justifications
+6. Validate: `./scripts/validate-appstore.sh`
+7. Run final validation before release: `./scripts/validate-appstore.sh --enforce-risk-docs`