feat: initial github-to-signal webhook server

HTTP server that receives GitHub webhook events and sends formatted
notifications to Signal via signal-cli's JSON-RPC API.

Supported events: push, issues, issue comments, pull requests,
PR reviews, PR review comments, releases, stars, forks, workflow
runs, branch/tag creation, branch/tag deletion.

Uses cbrgm/githubevents for webhook handling and taigrr/signalcli
for Signal delivery. Config via TOML file or GH2SIG_ env vars
(powered by taigrr/jety).

README.md

@@ -0,0 +1,19 @@
+# github-to-signal
+
+HTTP server that receives GitHub webhook events and forwards them as Signal messages via [signal-cli](https://github.com/AsamK/signal-cli).
+
+## Events
+
+Push, issues, issue comments, pull requests, PR reviews, PR review comments, releases, stars, forks, workflow runs, branch/tag creation and deletion.
+
+## Setup
+
+1. Copy `config.example.toml` to `config.toml` and fill in values
+2. Run the server: `go run .`
+3. Add a webhook in your GitHub repo pointing to `https://your-host:9900/webhook`
+
+All config values can also be set via environment variables with `GH2SIG_` prefix (e.g. `GH2SIG_SIGNAL_ACCOUNT`).
+
+## Requirements
+
+- [signal-cli](https://github.com/AsamK/signal-cli) running in daemon mode with JSON-RPC enabled