Fix LinkedIn session validation and auto-reconnect on expiry

[hasanMasalha]

Problem

Two bugs in LinkedIn session management:

Bug 1: Profile page shows "Connected" even when the LinkedIn session cookie has expired. The check only verifies the browser_profile/{user_id}/ folder exists — not whether the stored cookies are still valid.

Bug 2: When Easy Apply detects an expired session, it shows a generic error but gives the user no clear path to reconnect.

Fix

1. Add real session validation via headless Playwright (/feed redirect test)
2. Profile page calls real validation endpoint on load with loading state
3. Apply flow returns session_expired status with reconnect action
4. Apply page shows amber banner with direct reconnect link