Add compact pi-goal status UI and observability integration

[spences10]

Parent

• Epic/RFC: goal-directed task graph for my-pi #476

Depends on

• Add branch-aware pi-goal session persistence and recovery #478
• Expose pi-goal commands and graph-management tools #479

Scope

Show concise goal and graph status without replacing or conflicting with the existing footer. Use existing supported event and telemetry surfaces only.

Acceptance criteria

• Interactive status shows goal state and task counts without becoming a state store.
• UI is a no-op in print, JSON, and RPC modes where appropriate.
• The existing footer remains authoritative for footer layout.
• No new telemetry schema is introduced.
• Tests cover cleanup, session switches, terminal state, and non-interactive modes.