refactor(think-mode): migrate hook from chat.params to chat.message and remove thinking config injection

Drop provider-specific thinking config injection (THINKING_CONFIGS, getThinkingConfig,
resolveProvider) and instead rely on the provider to handle thinking based on the variant field.
Hook now fires on chat.message using model from input rather than from the message object.

🤖 Generated with assistance of [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/plugin/chat-message.ts

@@ -100,6 +100,7 @@ export function createChatMessageHandler(args: {
     await hooks.backgroundNotificationHook?.["chat.message"]?.(input, output)
     await hooks.runtimeFallback?.["chat.message"]?.(input, output)
     await hooks.keywordDetector?.["chat.message"]?.(input, output)
+    await hooks.thinkMode?.["chat.message"]?.(input, output)
     await hooks.claudeCodeHooks?.["chat.message"]?.(input, output)
     await hooks.autoSlashCommand?.["chat.message"]?.(input, output)
     await hooks.noSisyphusGpt?.["chat.message"]?.(input, output)