chore: add AGENTS.md for Cursor Cloud dev environment setup

[NITISH-R-G]

Description

Adds AGENTS.md with Cursor Cloud-specific development instructions for future cloud agents. This documents:

• Flutter SDK version requirements (3.41.9 / Dart 3.11.5)
• Key development commands (lint, test, build, serve)
• Environment file setup (assets/env.template → assets/.env)
• How to build/serve the Flutter web app with --dart-define for Supabase credentials
• Testing without external services (offline fallback demo)
• Known gotchas (BLE plugin warnings, localization warnings, Wasm warnings, asset serving path)

Type of change

• Documentation update

How Has This Been Tested?

Verified the full development workflow on a Cursor Cloud VM:

• Unit Tests — flutter test (14/14 pass)
• Manual Smoke Test — Demo page and Flutter web app tested end-to-end

Evidence

Flutter web app walkthrough — onboarding, SOS dashboard, safety tools, settings:

Main SOS dashboard with emergency button:

Safety tools screen:

Demo page offline triage — Severity 5 LIFE-THREATENING:
demo_offline_triage_hello_world.mp4

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes