feat: use local time as default for new activities

[marcosdsanchez]

PR Description

Title

feat: use local time as default for new activities

Description

This PR updates the default time for new activities to use the user's current local time instead of a fixed 4:00 PM (16:00).

Changes applied to:

• src/pages/activity/components/activity-form.tsx (Desktop Activity Form)
• src/pages/activity/activity-manager-page.tsx (Activity Manager Page)
• src/pages/activity/components/mobile-forms/mobile-activity-form.tsx (Mobile Activity Form)

Motivation

Previously, all new activities defaulted to 4:00 PM (market close time). While this might be suitable for some stock trades, it is often inaccurate for other types of activities, particularly cash transactions (deposits, withdrawals, transfers) which happen at specific times throughout the day.

By using the local time:

• Users get a more accurate default timestamp for their activities.
• It reduces the friction of having to manually adjust the time for every transaction that didn't happen exactly at market close.
• It improves the tracking of cash flows and intraday balances.

Verification

• Verified that clicking "Add Activity" on desktop now presets the date/time picker to the current local time.
• Verified that the mobile activity form also defaults to the current local time.
• Verified that the standalone Activity Manager page respects the local time default.