fix(build): add wrangler.build.toml for CI and fix autoconfig

Wrangler 4.94+ introduced --experimental-autoconfig (default: true) which
fails in non-interactive CI environments. Without a committed wrangler.toml,
the release action build was broken.

- Add wrangler.build.toml with minimal config (placeholder KV ID, no secrets)
- Update build script to use wrangler.build.toml + --no-experimental-autoconfig

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

wrangler.build.toml

@@ -0,0 +1,13 @@
+name = "kill-the-news"
+main = "src/index.ts"
+compatibility_date = "2025-01-01"
+compatibility_flags = ["nodejs_compat"]
+
+kv_namespaces = [
+  { binding = "EMAIL_STORAGE", id = "00000000000000000000000000000000" }
+]
+
+[[rules]]
+type = "Text"
+globs = ["**/*.css"]
+fallthrough = false