[Logic] Add timestamp tracking to all storage entries

[AbelOsaretin]

Description

None of the storage entries (projects, investments, whitelist) track when they were created or last modified. Timestamps would enable:

• Time-based queries and analytics
• Audit trails
• Time-based business logic (e.g., maturity dates)

Current Code Locations

• project_registry/src/types.rs — ProjectData
• investment_vault/src/types.rs — VaultKey

Recommendation

• Add created_at: u64 and updated_at: u64 fields to ProjectData
• Add timestamp to investment records
• Use env.ledger().timestamp() for consistent timestamps

Severity

Low — Improves auditability and enables time-based features.