feat: Improve some designs and sense

[jspw]

Summary

Improve the project dashboard and project detail experience with clearer information architecture, better selected-state/navigation feedback, first-class support for plan files, stronger memory/todo/commit views, more accurate cost aggregation, and clearer documentation that token/cost data is locally derived and estimated.

Closes #

Changes

• Redesigned the project detail navigation into clearer grouped tabs with improved naming and ordering to better match Claude Code concepts and user workflows
• Added and polished new project detail tabs/content for plans, memory, todos, commits, settings/automation, and related project context views
• Improved the memory tab UX so MEMORY.md acts as the primary source of truth and markdown references open the related memory entry preview
• Added first-class plan file discovery/parsing in the backend and surfaced plans in the project detail UI
• Improved the todos view to make the source session, timing, and status counts much easier to understand at a glance
• Polished the commits view spacing and section structure for better readability
• Added selected-project state to the sidebar so the currently opened project is clearly indicated
• Refreshed the main dashboard/home view so it feels visually consistent with the newer project detail experience
• Fixed dashboard/store cost aggregation so totals consistently include subagent cost where appropriate
• Updated UI labels and helper text to clearly communicate that token usage comes from local Claude session logs and cost is an estimate based on detected model pricing
• Added and updated unit tests across parsers, store logic, extension/sidebar flows, and webview UI views/components
• Updated project documentation to explain token/cost calculation behavior and estimation limits more accurately

Type of change

• Bug fix
• New feature
• Improvement / refactor
• Documentation
• Chore / dependency update

Testing

• Tested in Extension Development Host (F5)
• Verified existing functionality is not broken
• Added/updated tests (if applicable)

UI changes

• No UI changes in this PR
• Follows the design system (VS Code CSS variables, no hardcoded colors, no external UI libs) — run /ui-patterns for reference
• Tested on both dark and light VS Code themes

Checklist

• My code follows the project's coding conventions
• I have read the CONTRIBUTING guide
• No new dependencies added without discussion
• No console.log or debug statements left in