Modernize the web dashboard UI

[akhilsinghcodes]

This PR significantly refreshes the Agents Fleet web experience with a redesigned dashboard UI and related frontend improvements.

What changed

• Major App and Dashboard UI rewrite

  • Refactors and modernizes the main dashboard layout
  • Updates session list, session detail, and navigation behavior
  • Improves overall presentation and consistency across the app

• Improved chat session components

  • Updated ClaudeSdkChat and LiteLLMChat UI behavior to align with the new dashboard design
  • Refined interactions around session display and messaging

• Session artifacts and terminal panes

  • Updated SessionArtifacts to fit the redesigned UI
  • Adjusted TerminalPane behavior/appearance for the new layout

• Theme support

  • Added a shared theme.ts for centralized UI theming/styling concerns

• Dependency updates

  • Added/updated frontend dependencies and lockfile changes to support the UI refresh

Why this matters

This PR makes the product feel much more polished and cohesive, improving:

• dashboard readability
• session browsing and artifact inspection
• overall UX consistency
• maintainability of the web app UI layer

Scope

• Primarily frontend/UI changes under apps/web
• Includes updated theme support and dependency/lockfile changes
• No major backend API redesign in this commit