feat: add advanced search with single-level filter grouping and date filtering.

[suensky]

Features:

• Filter groups with AND/OR logic between and within groups
• Date filtering on Release Date (after/before operators)
• Month picker input for date selection
• Auto-creates placeholder group when opening empty Filters panel
• URL persistence for filter state (e.g., http://localhost:3000/?filters=OR%28provider%3Aequals%3Aanthropic%29%7EAND%7EOR%28releaseDate%3Aafter%3A2025-10%29)

Example queries:

• Query 1: (Provider = Anthropic OR OpenAI) AND (Reasoning = Yes)
• Query 2: (Release Date after 2025-01)

Tests: 64 unit tests covering evaluation, serialization, and date parsing.