Add NSFW-only filtering mode for content moderation

- Add nsfw_only_filtering field to GuildSettings model
- Create database migration for new field (20260124_add_nsfw_only_filtering)
- Update AI moderation logic to respect NSFW-only mode
- Add Discord command !ai nsfwonly <true/false> for toggling mode
- Implement filtering logic in image analysis for both attachments and embeds
- Add comprehensive test suite for new functionality
- Update documentation with usage examples and feature description
- Create dedicated CI workflow for testing NSFW-only filtering feature

When enabled, only sexual/nude content is filtered while allowing:
- Violence and gore
- Harassment and bullying
- Hate speech
- Self-harm content
- Other content categories

This mode is useful for gaming communities and mature discussion
servers that have specific content policies allowing violence
but prohibiting sexual material.

migrations/versions/20260124_add_nsfw_only_filtering.py

@@ -0,0 +1,39 @@
+"""Add nsfw_only_filtering column to guild_settings table.
+
+Revision ID: 20260124_add_nsfw_only_filtering
+Revises: 20260117_enable_ai_defaults
+Create Date: 2026-01-24 23:00:00.000000
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "20260124_add_nsfw_only_filtering"
+down_revision = "20260117_enable_ai_defaults"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    """Add nsfw_only_filtering column to guild_settings table."""
+    op.add_column(
+        "guild_settings",
+        sa.Column("nsfw_only_filtering", sa.Boolean, nullable=False, default=False)
+    )
+    
+    # Set default value for existing records
+    op.execute(
+        sa.text(
+            """
+            UPDATE guild_settings
+            SET nsfw_only_filtering = FALSE
+            WHERE nsfw_only_filtering IS NULL
+            """
+        )
+    )
+
+
+def downgrade() -> None:
+    """Remove nsfw_only_filtering column from guild_settings table."""
+    op.drop_column("guild_settings", "nsfw_only_filtering")