chore(scaffold): bootstrap docmost-sync Node/TS project skeleton

Set up the project structure per the new-project guide, adapted from the
Python skeleton to the Node/TS stack fixed in SPEC.md (reuses docmost-mcp).
Scaffold only — the sync engine is not implemented yet.

- src/settings.ts: single config layer on zod, schema keyed by real ENV
  names; credentials and own-service address have no default (fail fast).
- src/config-errors.ts: loadSettingsOrExit — clear startup message naming
  the missing/invalid env var instead of a raw stack trace; exit(1).
- src/index.ts: thin entry point that validates config and logs (stub).
- test/: vitest unit tests for settings parsing and config errors (10 tests).
- Makefile (install/env/build/test/run/dev/clean), strict tsconfig, vitest.
- Dockerfile (single-stage, no EXPOSE, prunes dev deps), docker-compose
  (daemon, volume on /app/data, watchtower), ghcr CI with build needs test.
- .env.example, .gitignore/.dockerignore, AGENTS.md, README.md.
- Pinned deps (dotenv, zod) + committed package-lock.json.

package.json

@@ -0,0 +1,28 @@
+{
+  "name": "docmost-sync",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "description": "Bidirectional sync daemon between Docmost articles and a local Markdown git vault.",
+  "license": "MIT",
+  "engines": {
+    "node": ">=20"
+  },
+  "scripts": {
+    "build": "tsc",
+    "start": "node build/index.js",
+    "dev": "tsx watch src/index.ts",
+    "test": "vitest run",
+    "test:watch": "vitest"
+  },
+  "dependencies": {
+    "dotenv": "17.4.2",
+    "zod": "3.25.76"
+  },
+  "devDependencies": {
+    "@types/node": "22.19.21",
+    "tsx": "4.22.4",
+    "typescript": "5.9.3",
+    "vitest": "3.2.6"
+  }
+}