Filippo/dashboard rid overview - #54

Related Issue:

(linka qui la task originale se esiste su Issues; altrimenti lascia vuoto o scrivi "Task assigned internally")

Description:

Replaces the "Work in progress" placeholder in src/app/dashboard/[rid]/page.tsx with a complete session-scoped dashboard: activity chart, stage+course summary panels, mocked automations section (structure ready for Inngest integration), and horizontally-scrollable latest applicants. Aggregation logic isolated in src/lib/services/dashboard.ts.

Guidelines Check:

• I ran pnpm dev and checked the results.
• I successfully ran pnpm build.
• I checked if there was something similar already that I could use, instead of creating it from scratch.
• I checked if I was following the same patterns as the other files and entities in the project (e.g. naming conventions).
• I verified that any AI-related software I used also followed these guidelines.