feat: enhance agent profile with availability status and signature

[Shindhu-Ramaswamy]

1.Agent Availability Status

Introduced an Availability Status field for agents (e.g. Available / Away).

This allows the system to clearly distinguish agents who are currently available to take tickets.

2. Agent Signature

Added a Signature field to the HD Agent doctype.

This can be used in ticket responses and communications.

3. Assignment UX Improvement

When assigning a ticket:

Only available agents are shown in the Assign To dropdown.

Prevents accidental assignment to away agents.

If an agent is marked as Away, a warning popup is shown during assignment.

4. Backend Filtering for Assign To

Implemented a custom assign_to_conditions override to ensure:

Agent filtering is enforced at the backend level.

Only agents with availability status = Available are returned in assignment queries.

#issue #2872 – Enhance Agent’s Profile

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.65%. Comparing base (d811720) to head (6d4192f).
⚠️ Report is 42 commits behind head on develop.

Files with missing lines	Patch %	Lines
helpdesk/helpdesk/doctype/hd_ticket/hd_ticket.py	66.66%	2 Missing ⚠️
helpdesk/overrides/assign.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3002      +/-   ##
===========================================
+ Coverage    50.56%   50.65%   +0.09%     
===========================================
  Files          122      123       +1     
  Lines         5403     5421      +18     
===========================================
+ Hits          2732     2746      +14     
- Misses        2671     2675       +4     

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