UI: Fix mobile header branding layout and align app identity with Swecha birds icon

Summary

This merge request fixes a mobile header layout issue and aligns app branding assets and naming across the application.

What does this MR do?

• Fixes mobile header grid behavior so the Swecha logo no longer drops under the app title.
• Keeps desktop header layout unchanged.
• Replaces the "ST" header mark with images/swecha-birds-icon.png.
• Renames app title from "Team Standup Tracker" to "Standup Tracker" in localized strings and document title.
• Adds favicon using images/swecha-birds-icon.png.

Related Issue

Closes #34 (closed)

How to Test

1. Run the app and open it in mobile viewport (<= 760px).
2. Verify header alignment: title, Swecha logo, and controls stay in a single row.
3. Switch to desktop viewport and confirm no layout regression.
4. Confirm header icon is the Swecha birds image.
5. Confirm app title reads "Standup Tracker".
6. Confirm browser tab favicon is the Swecha birds image.

Validation

• Production build passes successfully.

Checklist

• I have performed a self-review of my changes.
• I have tested the changes locally.
• I have verified there is no desktop regression.
• I have updated relevant UI text/resources.
• I have attached before/after screenshots (if required by reviewers).

Notes for Reviewers

Please verify responsive behavior on at least one mobile breakpoint and one desktop breakpoint.

After