Enforce baseline parity and add controlled tie-group variability to system prompt

[GVCUTV]

Motivation

• Align the system prompt with backend baseline intent by enforcing strict per-layer coverage ordering and deterministic reconciliation rules for scheduling output in src/main/resources/ai/system_prompt_template.txt.
• Prevent silent coverage masking and ensure uncovered slots are reported explicitly when hard-feasible candidates are exhausted.
• Introduce controlled, non-deterministic variability only for exact tie-groups to avoid predictable always-same doctor ordering while preserving hard constraints.

Description

• Replaced the previous deterministic tie-breakers block with STANDARD-BASELINE PARITY (NORMATIVE) which mandates filling ON_DUTY first then ON_CALL, enforces per-shift uniqueness, forbids cross-layer duplication, and requires exact role fidelity for emitted rows.
• Added explicit rules to recompute feasibility after each accepted assignment, to forbid reserving candidates across layers, and to preserve valid assignments while reporting uncovered (shift_id, required_role, assignment_status) keys when minima are unmet.
• Introduced CONTROLLED TIE VARIABILITY (NORMATIVE) that retains the existing ordered tie-resolution steps but replaces always-ascending doctor_id as the deterministic final step with a run-scoped seeded rotation/shuffle for exact tie-groups while forbidding any violation of hard constraints or layer-order rules.
• Added baseline parity examples, clarified emission statuses (e.g. PARTIAL_SUCCESS when reconciliation mismatches remain), and reinforced that SUCCESS is forbidden if layer minima are not satisfied.

Testing

• No automated tests were run as part of this change.

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Codex Task