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).

go.mod

@@ -0,0 +1,18 @@
+module github.com/taigrr/github-to-signal
+
+go 1.26.0
+
+require (
+	github.com/cbrgm/githubevents/v2 v2.2.0
+	github.com/google/go-github/v70 v70.0.0
+	github.com/taigrr/jety v0.2.0
+	github.com/taigrr/signalcli v0.0.0-20260301154901-6aed09f3f2af
+)
+
+require (
+	github.com/BurntSushi/toml v1.6.0 // indirect
+	github.com/google/go-querystring v1.2.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	golang.org/x/sync v0.12.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)