feat: multi-provider model configuration with UI/UX improvements (#355)

* feat: add multi-provider model configuration

- Add model config dialog for managing multiple AI providers
- Support for OpenAI, Anthropic, Google, Azure, Bedrock, OpenRouter, DeepSeek, SiliconFlow, Ollama, and AI Gateway
- Add model selector dropdown in chat panel header
- Add API key validation endpoint
- Add custom model ID input with keyboard navigation
- Fix hover highlight in Command component
- Add suggested models for each provider including latest Claude 4.5 series
- Store configuration locally in browser

* feat: improve model config UI and move selector to chat input

- Move model selector from header to chat input (left of send button)
- Add per-model validation status (queued, running, valid, invalid)
- Filter model selector to only show verified models
- Add editable model IDs in config dialog
- Add custom model input field alongside suggested models dropdown
- Fix hover states on provider buttons and select triggers
- Update OpenAI suggested models with GPT-5 series
- Add alert-dialog component for delete confirmation

* refactor: revert shadcn component changes, apply hover fix at usage site

* feat: add AWS credentials support for Bedrock provider

- Add AWS Access Key ID, Secret Access Key, Region fields for Bedrock
- Show different credential fields based on provider type
- Update validation API to handle Bedrock with AWS credentials
- Add region selector with common AWS regions

* fix: reset Test button after validation completes

* fix: reset validation button to Test after success

* fix: complete bedrock support and UI/UX improvements

- Add bedrock to ALLOWED_CLIENT_PROVIDERS for client credentials
- Pass AWS credentials through full chain (headers → API → provider)
- Replace non-existent GPT-5 models with real ones (o1, o3-mini)
- Add accessibility: aria-labels, focus-visible rings, inline errors
- Add more AWS regions (Ohio, London, Paris, Mumbai, Seoul, São Paulo)
- Fix setTimeout cleanup with useRef on component unmount
- Fix TypeScript type consistency in getSelectedAIConfig fallback

* chore: remove unused code

- Remove unused setAccessCodeRequired state in chat-panel.tsx
- Remove unused getSelectedModel export in model-config.ts

* fix: UI/UX improvements for model configuration dialog

- Add gradient header styling with icon badge
- Change Configuration section icon from Key to Settings2
- Add duplicate model detection with warning banner and inline removal
- Filter out already-added models from suggestions dropdown
- Add type-to-confirm for deleting providers with 3+ models
- Enhance delete confirmation dialog with warning icon
- Improve model selector discoverability (show model name + chevron)
- Add truncation for long model names with title tooltip
- Remove AI provider settings from Settings dialog (now in Model Config)
- Extract ValidationButton into reusable component

* fix: prevent duplicate model IDs within same provider

- Block adding model if ID already exists in provider
- Block editing model ID to match existing model in provider

* fix: improve duplicate model ID notifications

- Add toast notification when trying to add duplicate model
- Allow free typing when editing model ID, validate on blur
- Show warning toast instead of blocking input

* fix: improve duplicate model validation UX in config dialog

- Add inline error display for duplicate model IDs
- Show red border on input when error exists
- Validate on blur with shake animation for edit errors
- Prevent saving empty model names
- Clear errors when user starts typing
- Simplify error styling (small red text, no heavy chips)

lib/i18n/dictionaries/en.json

@@ -180,5 +180,24 @@
         "seekingSponsorship": "Call for Sponsorship",
         "contactMe": "Contact Me",
         "usageNotice": "Due to high usage, I have changed the model from Claude to minimax-m2 and added some usage limits. See About page for details."
+    },
+    "modelConfig": {
+        "title": "AI Model Configuration",
+        "description": "Configure multiple AI providers and models",
+        "configure": "Configure",
+        "addProvider": "Add Provider",
+        "addModel": "Add Model",
+        "modelId": "Model ID",
+        "modelLabel": "Display Label",
+        "streaming": "Enable Streaming",
+        "deleteProvider": "Delete Provider",
+        "deleteModel": "Delete Model",
+        "noModels": "No models configured. Add a model to get started.",
+        "selectProvider": "Select a provider or add a new one",
+        "configureMultiple": "Configure multiple AI providers and switch between them easily",
+        "apiKeyStored": "API keys are stored locally in your browser",
+        "test": "Test",
+        "validationError": "Validation failed",
+        "addModelFirst": "Add at least one model to validate"
     }
 }