[Feature] Introduce "App Type" option - generate real-world project templates

[Arjun544]

Overview

Currently FlutterInit generates a bare-bones app with onboarding, auth, and
a blank home screen. This is not enough for developers who want to hit the
ground running on a real project.

This issue introduces a new "App Type" config option that lets users select
what kind of app they are building. FlutterInit will then generate a
fully-structured, real-world project for that app type, not just folders,
but working screens, models, and logic scaffolded for that domain.

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App Type System

The appType option must be data-driven, not hardcoded. Each app type is a
self-contained template bundle that lives in templates/flutter/apps/.

New app types should be addable by simply dropping a new folder into
templates/flutter/apps/ and registering it, zero changes to the generator
core required. This makes app types a natural contribution surface for the
community.

Initial app types shipped with this feature:

• todo - Task management app
• ecommerce - Product listing, cart, checkout, orders
• chat - Conversations, messages, contacts
• fintech - Wallet, transactions, send/receive money

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What Each App Type Should Generate

Todo

• Task model (id, title, description, dueDate, isCompleted)
• Task list screen
• Create/edit task screen
• Filter by status (all, active, completed)
• Local persistence (Hive or SharedPreferences)

E-commerce

• Product model (id, name, price, images, category)
• Product listing screen with search & filter
• Product detail screen
• Cart screen
• Checkout screen
• Order history screen

Chat

• Message model (id, senderId, content, timestamp, type)
• Conversation list screen
• Chat screen with message bubbles
• Contact/user search screen
• Real-time ready structure (WebSocket or Supabase Realtime hooks)

Fintech

• Transaction model (id, amount, type, status, timestamp)
• Wallet/balance screen
• Transaction history screen
• Send money screen
• Receive money screen
• PIN/biometric auth hook

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Implementation Plan

1. Schema

• Add appType field to app/lib/config/schema.ts
• Update web dashboard UI to show the App Type selector
• Pass appType flag through generator to templates

2. Templates

• Create templates/flutter/apps/ as the root for all app bundles
• Each app folder mirrors the standard template structure but with
  domain-specific screens, models, and logic
• Registering a new app type should require no core generator changes

3. Generator Logic

• Update app/lib/ generator to dynamically load the correct app
  bundle based on appType
• Ensure all existing flags (architecture, state management, routing,
  theme) compose correctly on top of any app type

4. Quality

• dart analyze passes with zero errors for every app type
• Test all app types × all architectures (Clean, MVVM, Feature-First)