Redesign dashboard and break usage down by project

[MayankBansal12]

Summary

Reworks the usage dashboard around a new project dimension, so usage can be grouped by model, project, or day — not just agent or provider.

Project breakdown

• Every usage record now carries a project label derived from the working directory's final segment (e.g. bb-plugin-usage). The full path is never stored or transferred.
• All collectors extract the project: Codex (cwd in session metadata), Claude Code, Grok Agent, Pi/Prime (session cwd), and the host JSON collector.
• The host collector's cache version bumps to 3 so existing aggregates are re-scanned with project labels.
• Adds a project column to usage_events with its own index, plus a migration for existing databases; dashboard aggregation groups by project alongside day, provider, machine, and model.
• The dashboard's breakdown toggle gains a "Project" option between Model and Day.

Local currency

• USD costs show a tooltip with the equivalent in the browser's local currency. Rates come from open.er-api.com at runtime, cached in memory for 6 hours; any failure falls back to plain USD display.

Visual refresh

• New ProviderLogo component with brand marks and chart accent colors, replacing the inline color map.
• Segmented toggles get a sliding active indicator instead of per-button styling.
• Updated loading skeleton to match the new layout.