feat(dev): add one-command local Stalwart test server + workflow docs

Add docker-compose.yml: a disposable Stalwart instance with a fixed dev
admin account (STALWART_RECOVERY_ADMIN), matching the credentials
scripts/dev-token.ps1 already expected. Wired up via new npm scripts
(dev:server, dev:server:down, dev:server:logs).

scripts/dev-token.ps1 was previously untracked (the whole scripts/
directory was gitignored) even though it's part of the documented dev
workflow — un-ignored it, and added scripts/dev-token.sh, a POSIX
equivalent for non-Windows shells and AI agents without PowerShell.

New DEVELOPMENT.md documents the full loop end-to-end (start server,
get a token, run the dev server, verify), written so it's actionable by
both humans and AI coding agents without needing a browser. Linked from
AGENTS.md (Commands) and README.md (Getting started).

Verified manually: docker compose up brings the server to a healthy
state, /api/auth + /auth/token issue a working bearer token, and
/jmap/session returns 200 with it end-to-end.

package.json

@@ -6,6 +6,9 @@
   "type": "module",
   "scripts": {
     "dev": "vite",
+    "dev:server": "docker compose up -d",
+    "dev:server:down": "docker compose down",
+    "dev:server:logs": "docker compose logs -f stalwart",
     "build": "tsc -b && vite build",
     "typecheck": "tsc -p tsconfig.app.json --noEmit",
     "lint": "eslint .",