feat: rewrite gh-commit in Go with local Ollama backend

Replaces the Python/Crush/DuckDB implementation with a CGO-free Go binary:
cobra CLI, modernc.org/sqlite storage, huh/lipgloss UI, and speed-tuned raw
/api/generate calls (think:false, keep_alive, capped num_predict) against a
local qwen3.5:2b. Ships as a gh extension via cli/gh-extension-precompile.

main.go

@@ -0,0 +1,10 @@
+package main
+
+import "github.com/prdlk/gh-commit/cmd"
+
+// version is injected at release time via -ldflags "-X main.version=...".
+var version = "dev"
+
+func main() {
+	cmd.Execute(version)
+}