Rebuild webhooktimer from scratch with lightweight scheduler and minimal UI

[cto-new]

Summary

Rebuilt the project end-to-end with a new implementation focused on simplicity, robustness, and low resource usage.

Core backend rewrite

• Replaced the previous SQLite + dependency-heavy stack with a pure Go standard-library architecture.
• Added a new in-memory scheduler manager with durable JSON persistence:
  • Fixed interval mode
  • Random interval mode (min/max)
  • Sleep window support (including overnight ranges like 23:00 -> 06:00)
  • Per-entry enable/disable
  • Manual execute-now API with immediate result payload
  • Last execution timestamp + status tracking
  • Per-entry execution logs retained to last 10 entries
• Added per-entry execution locking to avoid overlapping webhook calls for the same entry.
• Added graceful shutdown and hardened HTTP server timeouts.

Storage/persistence

• Introduced atomic JSON state file persistence (STATE_PATH, default /data/state.json).
• State writes are done via temp file + rename for resilience.
• Runtime-only countdown state is kept in memory and not persisted.
• Old DB compatibility intentionally dropped (per ticket allowance).

API redesign

Implemented a new minimal API surface used by the UI:

• GET /api/entries
• POST /api/entries
• PUT /api/entries/{id}
• DELETE /api/entries/{id}
• POST /api/entries/{id}/toggle
• POST /api/entries/{id}/execute
• GET /api/entries/{id}/logs
• GET /healthz

Frontend rewrite

• Replaced the previous UI with a new dependency-free single-page interface (web/index.html):
  • Minimal, intuitive form for create/edit
  • Fixed/random interval controls
  • Sleep window controls
  • Entry enable/disable toggles
  • Live countdown display (updates every second)
  • Last execution display
  • Per-entry logs display (up to 10)
  • Run now button with immediate toast feedback

Container and footprint

• Replaced runtime image with a scratch-based static binary image.
• Added CA bundle copy for HTTPS webhook support.
• Added .dockerignore to reduce build context.
• Updated docker-compose.yml env vars to new state settings.

Documentation and repo hygiene

• Updated README for the rebuilt architecture and new configuration.
• Updated .gitignore for data/state artifacts.
• Removed old implementation packages/files and go.sum/dependency chain.

Validation performed

• Built and ran with Docker Compose successfully.
• Verified runtime image footprint is ~9 MB (well below 35 MB target).
• Performed browser validation using agent-browser:
  • Created entry
  • Observed entry rendering/countdown behavior
  • Triggered execute-now and confirmed immediate result + log update
  • Toggled entry enabled/disabled and confirmed UI/state changes

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