Resolve bugs relating to unexpected activity date changes.

[smorar]

Resolves #283 and #215 by:

• Create tz_applied fields in the schema object.
• Only apply timezone adjustments to the tz_applied fields.
• Changed references to start_time and created_at to use their corresponding tz_applied fields.

[Copilot]

Pull Request Overview

This PR fixes timezone-related bugs by introducing separate timezone-applied fields and preserving original timestamps. The changes ensure that date/time displays use timezone-adjusted values while maintaining original timestamps for data integrity.

• Added tz_applied fields to the activity schema for timezone-adjusted timestamps
• Updated frontend components to display timezone-adjusted dates instead of raw timestamps
• Modified backend to populate both original and timezone-adjusted timestamp fields

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
backend/app/activities/activity/schema.py	Added new tz_applied fields for start_time, end_time, and created_at
backend/app/activities/activity/utils.py	Modified to populate both original and tz_applied timestamp fields
frontend/app/src/views/SearchView.vue	Updated to use tz_applied fields for date display
frontend/app/src/views/Gears/GearView.vue	Updated to use tz_applied fields for activity timestamps
frontend/app/src/components/Gears/GearComponentListComponent.vue	Updated date comparisons to use tz_applied fields
frontend/app/src/components/Activities/ActivitySummaryComponent.vue	Updated to display tz_applied timestamps
frontend/app/src/components/Activities/ActivitiesTableRowComponent.vue	Updated table display to use tz_applied timestamps

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