perf: optimize event filtering with indexing

[anxkhn]

Problem Description

Event filtering uses linear search which is inefficient for large datasets.

Context

As the number of events grows, filtering performance will degrade.

Files to Investigate

• src/lib/store.ts - getFiltered method

Expected Behavior

Filtering should use indexed lookups for better performance.

Acceptance Criteria

• Add indexes for commonly filtered fields
• Filter complexity reduced from O(n)
• Add performance tests

Suggested Approach

Implement Map-based indexes for category, status, and other filterable fields.

Difficulty: Medium

Estimated time: 1-2 hours
Prerequisites: Data structures, algorithm complexity
Learning outcomes: Performance optimization