feat: implement real-time collaborative task editing with presence indicators (#2933)

[desireddymohithreddy0925]

Summary

Adds live presence indicators and collaborative editing sync to task pages, preventing conflicting updates when multiple team members view the same task.

Closes #2933

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Type of Change

• ✨ New feature (non-breaking change that adds functionality)

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What Changed

• Integrated Supabase Realtime Channels for presence broadcasting.
• Added user avatar indicators to the top of task pages showing active viewers.
• Implemented a "Currently editing" warning when another user modifies a field simultaneously.

[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus