feat (user counert): add active_sessions table for counter

[YNazymko12]

• Add active_sessions schema with session tracking
• Add index on last_activity for performance optimization
• Prepare database structure for live online user counter

Table structure:

• session_id (text, PK): unique session identifier
• last_activity (timestamp): tracks user's last activity time

Migration file: drizzle/0002_clean_martin_li.sql

Related to: (SP: 3) [Frontend + Backend] Track all active users and display live online counter on Home page

Summary by CodeRabbit

Release Notes

• New Features
  • Implemented active session tracking to monitor and manage user session activity, enhancing system reliability and session handling capabilities.

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[coderabbitai]

📝 Walkthrough

Walkthrough

These changes introduce a new active_sessions database table to the frontend schema using drizzle-orm. The changes include TypeScript schema definitions, SQL migration, schema metadata snapshot, and journal entry.

Changes

Cohort / File(s)	Summary
Schema Definitions frontend/db/schema/index.ts, frontend/db/schema/sessions.ts	Added new sessions schema module with export. New sessions.ts defines activeSessions table with sessionId (primary key) and lastActivity (timestamp, defaults to now). Updated index export to include sessions and changed quote style.
Database Migration frontend/drizzle/0002_clean_martin_li.sql	SQL migration creating active_sessions table with session_id (text, primary key) and last_activity (timestamp, not null, default now()). Includes B-tree index on last_activity.
Migration Metadata frontend/drizzle/meta/0002_snapshot.json, frontend/drizzle/meta/_journal.json	Added comprehensive schema snapshot capturing full database model structure. Journal entry records migration metadata with tag "0002_clean_martin_li" and timestamp.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested reviewers

• ViktorSvertoka
• AM1007

Poem

A sessions table, fresh and new,
With timestamps tracking what we do,
From schema file to SQL's embrace,
The database finds its proper place. 🐰✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title mentions 'user counert' (apparent typo for 'counter') and references adding active_sessions table, which aligns with the PR's main objective of adding a sessions table for a live user counter.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

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