Bootstrap Go module + Cloudflare Worker build tooling (#21)

Initialize the Go module and the Go -> Cloudflare Workers (TinyGo/Wasm) build
path, structured so `go test` and a local dev server run on plain Go without
TinyGo, while the real Wasm entrypoint is isolated behind build tags.

- go.mod/go.sum: module github.com/JMR-dev/LibreMail-Bug-Report-Ingest (Go 1.26),
  requiring github.com/syumai/workers.
- internal/handler: build-tag-free core http.Handler (GET / and GET /healthz,
  JSON responses, 404/405 handling) with net/http/httptest unit tests.
- cmd/devserver: plain net/http server mounting the core handler for local dev
  without TinyGo (listens on :8787, override with ADDR).
- worker/main.go: Cloudflare Workers (Wasm) entrypoint behind
  //go:build js && wasm, wiring the same handler via github.com/syumai/workers;
  excluded from host builds/tests.
- package.json + pnpm-lock.yaml + pnpm-workspace.yaml: wrangler dev dependency
  managed with pnpm, with toolchain build scripts approved.
- wrangler.jsonc: name=libremail-bug-report-ingest, main=./build/worker.mjs,
  build via `pnpm run build` (TinyGo).
- README: "Build & run locally" section with exact commands and the rationale
  for the TinyGo + syumai/workers path.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

cmd/devserver/main.go

@@ -0,0 +1,28 @@
+// Command devserver runs the core bug-report ingest handler on a plain
+// net/http server for local development.
+//
+// It deliberately does not depend on TinyGo or the Cloudflare Workers runtime,
+// so `go run ./cmd/devserver` works with the standard Go toolchain and exercises
+// the exact same handler that the deployed Wasm Worker serves. It listens on
+// :8787 by default (matching wrangler dev's default port); override with ADDR.
+package main
+
+import (
+	"log"
+	"net/http"
+	"os"
+
+	"github.com/JMR-dev/LibreMail-Bug-Report-Ingest/internal/handler"
+)
+
+func main() {
+	addr := os.Getenv("ADDR")
+	if addr == "" {
+		addr = ":8787"
+	}
+
+	log.Printf("devserver listening on %s (try GET / and GET /healthz)", addr)
+	if err := http.ListenAndServe(addr, handler.New()); err != nil {
+		log.Fatalf("devserver: %v", err)
+	}
+}