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.

test/settings.test.ts

@@ -0,0 +1,76 @@
+import { describe, expect, it } from 'vitest';
+import { parseSettings } from '../src/settings.js';
+
+// A minimal valid environment with every required variable set. Tests clone and
+// mutate this object so process.env is never touched (hermetic).
+const baseEnv = {
+  DOCMOST_API_URL: 'https://docmost.example.com',
+  DOCMOST_EMAIL: 'you@example.com',
+  DOCMOST_PASSWORD: 'secret',
+  DOCMOST_SPACE_ID: 'space-123',
+} as NodeJS.ProcessEnv;
+
+describe('parseSettings', () => {
+  it('maps a full valid env to the camelCase Settings object', () => {
+    const settings = parseSettings({
+      ...baseEnv,
+      VAULT_PATH: 'data/custom-vault',
+      GIT_REMOTE: 'git@github.com:you/vault.git',
+      POLL_INTERVAL_MS: '5000',
+      DEBOUNCE_MS: '1000',
+      LOG_LEVEL: 'debug',
+    });
+
+    expect(settings).toEqual({
+      docmostApiUrl: 'https://docmost.example.com',
+      docmostEmail: 'you@example.com',
+      docmostPassword: 'secret',
+      docmostSpaceId: 'space-123',
+      vaultPath: 'data/custom-vault',
+      gitRemote: 'git@github.com:you/vault.git',
+      pollIntervalMs: 5000,
+      debounceMs: 1000,
+      logLevel: 'debug',
+    });
+  });
+
+  it('applies defaults when optional vars are omitted', () => {
+    const settings = parseSettings({ ...baseEnv });
+
+    expect(settings.vaultPath).toBe('data/vault');
+    expect(settings.pollIntervalMs).toBe(15000);
+    expect(settings.debounceMs).toBe(2000);
+    expect(settings.logLevel).toBe('info');
+    expect(settings.gitRemote).toBeUndefined();
+  });
+
+  it('coerces numeric strings to numbers', () => {
+    const settings = parseSettings({ ...baseEnv, POLL_INTERVAL_MS: '3000' });
+
+    expect(settings.pollIntervalMs).toBe(3000);
+    expect(typeof settings.pollIntervalMs).toBe('number');
+  });
+
+  it('throws when a required var is missing', () => {
+    const { DOCMOST_API_URL: _omit, ...rest } = baseEnv;
+    void _omit;
+    expect(() => parseSettings(rest as NodeJS.ProcessEnv)).toThrow();
+  });
+
+  it('throws on an invalid LOG_LEVEL', () => {
+    expect(() =>
+      parseSettings({ ...baseEnv, LOG_LEVEL: 'verbose' }),
+    ).toThrow();
+  });
+
+  it('throws on a non-numeric POLL_INTERVAL_MS', () => {
+    expect(() =>
+      parseSettings({ ...baseEnv, POLL_INTERVAL_MS: 'soon' }),
+    ).toThrow();
+  });
+
+  it('treats an empty GIT_REMOTE as undefined', () => {
+    const settings = parseSettings({ ...baseEnv, GIT_REMOTE: '' });
+    expect(settings.gitRemote).toBeUndefined();
+  });
+});