[Frontend] Fix welcome page, app-shell header, context nav links, and .env.example

[ibourgeois]

Problems

1. Broken link: welcome.blade.php links authenticated users to /dashboard which doesn't exist — app routes to /. Results in a 404.
2. Dark mode mismatch: welcome.blade.php uses Tailwind dark: classes (OS-level media query) while the rest of the app uses a data-theme="dark" custom variant. The user-controlled theme toggle has no effect on this page.
3. Hardcoded title: app-shell.blade.php renders <h1>Ideas</h1> on every page regardless of which section is active.
4. Context nav placeholder links: All context nav items (Inbox, Drafts, Shared, Proposals) in home.blade.php, ideas/index.blade.php, ideas/create.blade.php, and ideas/edit.blade.php point to route('ideas.index'). Clicking any of them navigates to the same page.
5. Missing AI env vars: AI_DEFAULT_PROVIDER, OLLAMA_API_KEY, OLLAMA_BASE_URL, and OLLAMA_MODEL are used in config/ai.php but not documented in .env.example.

Required Changes

• welcome.blade.php: change url('/dashboard') → route('home'); replace dark: classes with [data-theme=dark]: utility syntax
• app-shell.blade.php: add an $appTitle prop (default: 'Ideas') and use it in the <h1>
• Context nav: set "Drafts" → ideas.index; set unimplemented items (Inbox, Shared, Proposals) to #
• .env.example: document the four AI environment variables with comments

Files

• resources/views/welcome.blade.php
• resources/views/components/layouts/app-shell.blade.php
• resources/views/home.blade.php
• resources/views/ideas/index.blade.php
• resources/views/ideas/create.blade.php
• resources/views/ideas/edit.blade.php
• .env.example