feat: Collapsible right sidebar for workflow session details

[esnunes]

Summary

• Adds a collapsible right sidebar to the workflow session detail page (/sessions/:id) showing session info, project info, exported metadata (grouped by phase), and AI sessions with token usage
• Sidebar is open by default and persists collapsed/expanded state in localStorage via a colocated JS hook
• Sidebar content updates in real-time via PubSub (metadata changes, phase transitions)
• Not shown on type selection (/workflows) or pre-session Phase 1 pages

Changes

• lib/destila_web/live/workflow_runner_live.ex — Sidebar rendering, data loading, PubSub refresh handlers, helper functions for formatting dates/tokens/metadata
• lib/destila/workflows.ex — list_metadata_records/1 query returning structs grouped by phase
• lib/destila/ai.ex — list_ai_sessions_for_workflow/1 with ordered message preload; extract_token_usage/1 and aggregate_token_usage/1 helpers
• assets/css/app.css — Sidebar transition CSS (width, opacity, toggle icon visibility)
• test/destila_web/live/workflow_session_sidebar_test.exs — 11 tests covering all feature scenarios

Test plan

• Sidebar visible on session detail page
• Sidebar not rendered on type selection page
• Toggle button collapses/expands sidebar
• Session info shows dates and duration
• Completion date shown for done sessions
• Project name and repo URL displayed
• Metadata grouped by phase name
• Real-time metadata updates via PubSub
• AI sessions with status badges and token usage
• Empty states for no metadata / no AI sessions

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