v4: Browse, Explore refactor, AI reports, and DNA Chat improvements

[vishakh]

Navigation restructure

• Renamed pages: Explore to Browse, DNA Chat to Chat, Overview Report to Analyze
• Added a new Explore page as the primary results view: trait-by-trait navigation with elevated/protective signals ranked by effect size, and condition matching from health history
• Added "Continue in DNA Chat" from study pages

Browse (formerly Explore)

• Full study browser with filtering by trait, sample size, p-value, and significance
• Interactive heatmap showing SNP match density across selected studies
• Inline LLM study analysis and per-study commentary

AI Reports (Analyze page)

Three new AI-generated reports, all premium-gated:

• Health Insights Report: anchored to personal and family health history, surfaces genetic mechanisms and novel findings
• Healthspan Report: organizes results across six biological domains (cardiovascular, metabolic, neurological, immune, musculoskeletal, cancer susceptibility)
• Top Traits Report: synthesizes the 100 highest-signal associations by effect size into a biological portrait with personal hypotheses

All reports include:

• Suggested follow-up questions for DNA Chat
• Collapsible trait list showing which associations were used
• Copy, print, and "Discuss in DNA Chat" actions
• Comprehensive Overview Report moved to bottom of the page, marked experimental

DNA Chat improvements

• Dynamically generated follow-up questions after each response, context-aware and personalized to the user's profile
• Follow-up buttons now send the question directly rather than populating the input field
• Report context passed through to Chat when navigating from any report modal

Infrastructure

• nilAI 429 retry logic with 15s and 30s backoff over three attempts
• Google Analytics utility scripts for performance analysis
• LLM client improvements