feat: add real-time progress feedback for AI analysis

[crystalin]

Summary

• Adds step-based progress indicator to the AI analysis processing panel, showing clear stages: Queued → Generating → Results Ready
• Displays elapsed time counter during analysis processing so users know it's working
• Shows a success toast notification when analysis completes (auto-dismisses after 4 seconds)
• Smooth slide-in animation when transitioning from processing to completed state
• Detects stalled analyses: warns users when the worker hasn't picked up the job (>30s pending) or processing is taking too long (>3min)
• Stops polling after 5 minutes with a clear message instead of spinning forever
• Shows a Retry Analysis button when the analysis appears stalled

Before: Static "Analysis in progress..." message with no stage indication; users had to manually refresh to see results and could wait forever with no feedback.

After: Clear visual progress through stages with elapsed timer. Warning when analysis is stalled. Auto-stop polling with retry option. Toast notification when analysis is ready.

Changes

• services/dashboard/src/routes/partials/analysis.ts — Enhanced renderProcessingPanel with progress steps, timer, stalled detection, and retry button; added completion toast and animation to renderCompletedPanel
• docs/06-Reference/changelog.md — Added changelog entry

Test plan

• Trigger AI analysis on a conversation and verify progress steps show correctly
• Verify "Queued, waiting for worker..." shows initially, then transitions to "Generating analysis with AI..." when status changes to processing
• Verify elapsed time counter increments on each poll
• Verify amber warning appears after ~30s if analysis stays pending
• Verify polling stops after 5 minutes with "Polling stopped" message
• Verify "Retry Analysis" button appears when stalled and works correctly
• Verify success toast appears when analysis completes
• Verify toast auto-dismisses after ~4 seconds
• Verify no toast appears when viewing an already-completed analysis (page load)
• Verify regenerate still works correctly

🤖 Generated with Claude Code