Implement cache bypass period after calendar modifications #215
Description
Implement a cache bypass period for calendars similar to the solution in mergecal PR #236:
- Add a constant (e.g., CACHE_BYPASS_HOURS = 3) to control the bypass duration after a calendar is saved.
- Implement a method to determine if a calendar is within the bypass window (e.g., is_in_cache_bypass_period()).
- Add a method to get the end time of the cache bypass (e.g., get_cache_bypass_end_time()).
- When a calendar is modified, set response headers to disable caching for 3 hours (e.g., Cache-Control: max-age=0).
- (Optional) Pass bypass context to the frontend to display status/info for users.
This ensures users immediately see changes after saving, improving UX, while retaining caching benefits for stable calendars. See mergecal PR #236 for implementation details and rationale.