feat: event detail page styling and deleted events indicator

- Fix event detail page for direct navigation by using FastHTML's
  idiomatic htmx parameter instead of manual header check
- Add custom toaster.py with HTML support using NotStr to render
  clickable links in toast messages
- Add hx_preserve to toast container to survive HTMX body swaps
- Add is_deleted column to event_log_by_location table
- Update event_log projection revert() to set is_deleted flag
  instead of deleting rows
- Add strikethrough styling for deleted events in event log

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

migrations/0010-addeventlogisdeleted.sql

@@ -0,0 +1,4 @@
+-- ABOUTME: Migration 0010 - add_event_log_is_deleted
+-- ABOUTME: Adds is_deleted flag to event_log_by_location for deleted event visibility.
+
+ALTER TABLE event_log_by_location ADD COLUMN is_deleted INTEGER NOT NULL DEFAULT 0;