feat: presentation defaults + scheduler active-only

Add Settings → Events (Presentations) defaults (interval, page-progress,
auto-progress) persisted via /api/system-settings
Seed defaults in init_defaults.py (10/true/true)
Add Event.page_progress and Event.auto_progress (Alembic applied)
CustomEventModal applies defaults on create and saves fields
Scheduler publishes only currently active events per group, clears retained
topics when none, normalizes times to UTC; include flags in payloads
Docs: update README, copilot instructions, and DEV-CHANGELOG
If you can split the commit, even better

feat(dashboard): add presentation defaults UI
feat(api): seed presentation defaults in init_defaults.py
feat(model): add Event.page_progress and Event.auto_progress
feat(scheduler): publish only active events; clear retained topics; UTC
docs: update README and copilot-instructions
chore: update DEV-CHANGELOG

server/alembic/versions/910951fd300a_add_page_progress_and_auto_progress_to_.py

@@ -0,0 +1,34 @@
+"""Add page_progress and auto_progress to Event
+
+Revision ID: 910951fd300a
+Revises: 045626c9719a
+Create Date: 2025-10-18 11:59:25.224813
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '910951fd300a'
+down_revision: Union[str, None] = '045626c9719a'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column('events', sa.Column('page_progress', sa.Boolean(), nullable=True))
+    op.add_column('events', sa.Column('auto_progress', sa.Boolean(), nullable=True))
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column('events', 'auto_progress')
+    op.drop_column('events', 'page_progress')
+    # ### end Alembic commands ###