Implement organized media folder structure for community posts

- Add media_folder field to Post model for organized file storage
- Create MediaConfig class for centralized media management settings
- Update community routes to use post-specific media folders
- Add thumbnail generation for uploaded images
- Implement structured folder layout: app/static/media/posts/{post_folder}/
- Add utility functions for image and GPX file handling
- Create media management script for migration and maintenance
- Add proper file validation and MIME type checking
- Include routes for serving images, thumbnails, and GPX files
- Maintain backward compatibility with existing uploads
- Add comprehensive documentation and migration tools

Each post now gets its own media folder with subfolders for:
- images/ (with thumbnails/ subfolder)
- gpx/

Post content remains in database for optimal query performance while
media files are organized in dedicated folders for better management.

migrations/add_media_folder.py

@@ -0,0 +1,28 @@
+"""Add media_folder to posts table
+
+This migration adds a media_folder column to the posts table to support
+organized file storage for each post.
+
+Usage:
+    flask db upgrade
+
+Revision ID: add_media_folder
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers
+revision = 'add_media_folder'
+down_revision = None
+depends_on = None
+
+def upgrade():
+    """Add media_folder column to posts table"""
+    # Add the media_folder column
+    op.add_column('posts', sa.Column('media_folder', sa.String(100), nullable=True))
+
+def downgrade():
+    """Remove media_folder column from posts table"""
+    # Remove the media_folder column
+    op.drop_column('posts', 'media_folder')