fix: add username truncation for common dashboard dropdown

[Saksham-Sirohi]

Fixes part of #2965

Summary by Sourcery

New Features:

• Use a standardized short user label in the profile dropdown instead of the full name to improve layout in the common dashboard header.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Implements username truncation in the common profile dropdown by switching from displaying the full name directly to using a reusable short_user_label template filter, and ensuring the relevant template tag library is loaded.

File-Level Changes

Change	Details	Files
Use a reusable truncated/short username label in the common profile dropdown instead of the full name.	Load the custom event_tags template tag library in the common profile dropdown fragment so custom filters are available. Replace direct use of request.user.get_full_name with the short_user_label template filter on request.user within the dropdown summary.	app/eventyay/common/templates/common/fragment_profile_dropdown.html

Possibly linked issues

• #Truncate User Name in Dropdown Menu and Show First Name Only: The PR replaces full_name with short_user_label in the dropdown, implementing the issue’s truncated-first-name requirement.

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[sourcery-ai]

Hey - I've left some high level feedback:

• Consider exposing the full get_full_name via a title attribute or similar on the <summary> or icon so truncated labels remain accessible (e.g., for screen readers and hover tooltips).
• Ensure the short_user_label filter gracefully handles cases where request.user is anonymous or missing profile fields, since this template previously relied on get_full_name which is defined only for authenticated users.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider exposing the full `get_full_name` via a `title` attribute or similar on the `<summary>` or icon so truncated labels remain accessible (e.g., for screen readers and hover tooltips).
- Ensure the `short_user_label` filter gracefully handles cases where `request.user` is anonymous or missing profile fields, since this template previously relied on `get_full_name` which is defined only for authenticated users.

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[Saksham-Sirohi]

[ArnavBallinCode]

LGTM, this pr is only solving the username truncation issue from the entire issue, you could change it from fixes to partially solves