build: signed PGXN release tooling + Drone pipeline

Build the distribution from src/ (control, versioned SQL, META, MIT LICENSE,
PGXS Makefile, install README), checksum it, and sign an Ed25519 JWT manifest
(audience pgmorbac-release) with the verification public key attached to the
release. `npm run release` does it locally; the Drone pipeline does it on a
v* tag once the repo is Trusted with the pgmorbac_release_key + gitea_token
secrets.

package.json

@@ -0,0 +1,14 @@
+{
+  "name": "pgmorbac-release-tools",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "description": "Release tooling for the pgmorbac PostgreSQL extension (build + sign + publish the PGXN distribution).",
+  "scripts": {
+    "dist": "node scripts/build-dist.mjs",
+    "release": "node scripts/build-dist.mjs && node scripts/gitea-release.mjs"
+  },
+  "devDependencies": {
+    "jose": "^5"
+  }
+}