Onboarding: flag gating, resource setup and connection signal

[talissoncosta]

Part of #7737. The cross-cutting plumbing the parts depend on.

Scope

• Render behind the FoF flag (replace TEMP force) + percentage rollout.
• Idempotent resource bootstrap (org / project / Dev + Prod / first flag).
• Loading splash (lazy Lottie).
• Wire the real first-evaluation signal (Onboarding: track first SDK evaluation received #7623) into the terminal's connected state.

Done when

• Renders only behind the flag; revisits create no duplicate resources.
• Connected state fires from the real Onboarding: track first SDK evaluation received #7623 signal, never faked.

Depends on #7623, plus #7765 & #7766 for the components it assembles.