Add StartOS 0.3.5 compatibility

[kwsantiago]

Summary

Restores StartOS 0.3.5 compatibility files alongside the existing 0.4.x code, so both SDK versions can build from the same repo.

• Adds manifest.yaml, Dockerfile, instructions.md, and scripts/ for StartOS 0.3.5 builds
• Dockerfile extends binwiederhier/ntfy:v2.19.2 and installs bash, curl, and yq for the entrypoint
• docker_entrypoint.sh reads /data/start9/config.yaml and exports the corresponding NTFY_* env vars before exec ntfy serve
• Config UI exposes: Enable Signup, Base URL, Log Level, attachment size limits, and Cache Duration
• NTFY_BASE_URL defaults to http://localhost when unset (ntfy requires it whenever an attachment cache dir is configured)
• Health check hits /v1/health
• 0.4.x files under startos/ are untouched

I'm running StartOS 0.3.5 and built/tested the .s9pk successfully with start-sdk pack.

[kwsantiago]

Note: scripts/embassy.js is a build artifact from deno run scripts/bundle.ts - committed so start-sdk pack works without requiring Deno as a build dependency.