Enhance read_image tool with magic byte detection and multi-image support

- Fix media type detection using magic bytes instead of file extension
  - Correctly identifies JPEG files with .png extension (and vice versa)
  - Supports PNG, JPEG, GIF, and WebP formats

- Add multi-image support with file_paths array parameter
  - Load multiple images in a single tool call
  - All images queued for LLM analysis

- Enhanced CLI output:
  - Inline image preview via iTerm2 imgcat protocol (height=5)
  - Dimmed info line showing: path | dimensions | media type | file size
  - Proper │ prefix alignment with tool output boxing
  - Human-readable file sizes (bytes, KB, MB)

- Add image dimension extraction from file headers
  - PNG, JPEG, GIF, WebP dimension parsing

- Add comprehensive tests for magic byte detection and dimensions

crates/g3-core/src/prompts.rs

@@ -259,6 +259,10 @@ Short description for providers without native calling specs:
   - Example: {\"tool\": \"read_file\", \"args\": {\"file_path\": \"src/main.rs\"}
   - Example (partial): {\"tool\": \"read_file\", \"args\": {\"file_path\": \"large.log\", \"start\": 0, \"end\": 1000}
 
+- **read_image**: Read an image file for visual analysis (PNG, JPEG, GIF, WebP)
+  - Format: {\"tool\": \"read_image\", \"args\": {\"file_path\": \"path/to/image.png\"}}
+  - Example: {\"tool\": \"read_image\", \"args\": {\"file_path\": \"sprites/fairy.png\"}}
+
 - **write_file**: Write content to a file (creates or overwrites)
   - Format: {\"tool\": \"write_file\", \"args\": {\"file_path\": \"path/to/file\", \"content\": \"file content\"}
   - Example: {\"tool\": \"write_file\", \"args\": {\"file_path\": \"src/lib.rs\", \"content\": \"pub fn hello() {}\"}