Context

PR implementing #2408 (CraniMem goal-conditioned write gate) added goal_utility as a 6th admission factor and wired with_goal_gate() into AdmissionControl at bootstrap. However, remember() and remember_with_parts() in semantic/recall.rs currently always pass None for goal_text.

Required Change

In zeph-core, derive goal_text per-turn from:

• The system prompt's task description (if present)
• The most recent user message (as proxy for immediate intent)

Pass it through the agent context builder into SemanticMemory::remember() / remember_with_parts() so that AdmissionControl::evaluate() receives the goal context and can apply the goal-conditioned gate.

Acceptance Criteria

• goal_text is computed per-turn in context assembly
• Passed to remember() calls so goal gate is active when goal_conditioned_write = true
• Zero behavior change when goal_conditioned_write = false