Organize documentation: Move all .md files to readmes/ directory

readmes/REACTION_FEATURE.md

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+# Message Reaction Feature
+
+## Overview
+This feature allows you to make Miku react to any message in Discord with a specific emoji of your choice through the Web UI.
+
+## How to Use
+
+### From the Web UI
+
+1. **Navigate to the Actions Tab**
+   - Open the Miku Control Panel (http://your-server:3939)
+   - Click on the "Actions" tab
+
+2. **Find the "Add Reaction to Message" Section**
+   - Scroll down to find the "😊 Add Reaction to Message" section
+
+3. **Fill in the Required Information**
+   - **Message ID**: Right-click on the target message in Discord → "Copy ID"
+   - **Channel ID**: Right-click on the channel name → "Copy ID"
+   - **Emoji**: Enter the emoji you want Miku to react with (e.g., 💙, 👍, 🎉)
+
+4. **Click "Add Reaction"**
+   - Miku will add the specified reaction to the message
+   - You'll see a success confirmation message
+
+### Requirements
+
+- **Discord Developer Mode**: You need to enable Developer Mode in Discord to copy message and channel IDs
+  - Settings → Advanced → Developer Mode (toggle ON)
+
+### Supported Emoji Types
+
+- **Standard Unicode Emoji**: 💙, 👍, 🎉, ❤️, etc.
+- **Custom Server Emoji**: Use the format `:emoji_name:` for custom Discord emojis
+
+### API Endpoint
+
+If you want to integrate this programmatically:
+
+```bash
+POST /messages/react
+Content-Type: multipart/form-data
+
+message_id: <Discord message ID>
+channel_id: <Discord channel ID>
+emoji: <emoji string>
+```
+
+### Example Response
+
+Success:
+```json
+{
+  "status": "ok",
+  "message": "Reaction 💙 queued for message 123456789"
+}
+```
+
+Error:
+```json
+{
+  "status": "error",
+  "message": "Channel 123456789 not found"
+}
+```
+
+## Troubleshooting
+
+- **"Channel not found"**: Make sure Miku is in the server that contains that channel
+- **"Message not found"**: Verify the message ID is correct and still exists
+- **"Permission denied"**: Miku needs the "Add Reactions" permission in that channel
+- **Invalid emoji**: Make sure you're using a valid emoji format
+
+## Technical Details
+
+- The reaction is added asynchronously by the Discord bot
+- The Web UI receives immediate confirmation that the request was queued
+- If the reaction fails (e.g., due to permissions), an error will be logged in the bot logs