refactor: rename project from Freepik to Magnific

Rename all identifiers, strings, file names, env vars, CLI entry point,
ASCII banner, and API endpoint to reflect the company rebrand.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -1,11 +1,11 @@
-# Freepik API Configuration
-# Get your API key at https://www.freepik.com/api
-FREEPIK_API_KEY=your_api_key_here
+# Magnific API Configuration
+# Get your API key at https://magnific.ai
+MAGNIFIC_API_KEY=your_api_key_here
 
 # Optional overrides
-# FREEPIK_BASE_URL=https://api.freepik.com
-# FREEPIK_POLL_TIMEOUT=600
-# FREEPIK_DEFAULT_IMAGE_MODEL=flux-2-pro
-# FREEPIK_DEFAULT_VIDEO_MODEL=kling-o1-pro
-# FREEPIK_DEFAULT_OUTPUT_DIR=./output
-# FREEPIK_SHOW_BANNER=true
+# MAGNIFIC_BASE_URL=https://api.magnific.ai
+# MAGNIFIC_POLL_TIMEOUT=600
+# MAGNIFIC_DEFAULT_IMAGE_MODEL=flux-2-pro
+# MAGNIFIC_DEFAULT_VIDEO_MODEL=kling-o1-pro
+# MAGNIFIC_DEFAULT_OUTPUT_DIR=./output
+# MAGNIFIC_SHOW_BANNER=true