fix(session-store): prewarm exact voter transition authority

[VerifiedOrganic]

Outcome

Prewarms one exact authenticated voter roster before consumer activation and keeps protected fenced-transition calls on the local-fast authority path.

Safety

• Exact scope, voter, roster, server identity, and local SPIFFE binding
• N startup capability queries for N voters; no hot-path capability RPC
• Mixed-version activation fails before proposal
• Generic protected and remote-sealing checks remain fail-closed
• One physical proposal and one B1/P1 proof

Verification

Focused session-net/session-store behavioral tests, all-target clippy with warnings denied, formatting, diff check, and independent P0/P1 review passed.

[VerifiedOrganic]

Closing as superseded by the implementation already on main. A direct ancestry check against 1dff851430c5671993e68aa3d81889402f2f5034 confirms that the first six of this PR's seven commits are present, including a73519aa686a55c48e87df893499b81c1d621459 (exact voter transition prewarm authority). The sole non-ancestor commit, 2b329ef4, only adjusts old consumer test fixtures.

The current implementation and fixtures were subsequently revised by merged #717 and #745. Current consumer.rs has explicit regression coverage named prepared_cas_response_loss_warms_the_cold_receipt_voter, prepared_cas_cold_setup_precedes_the_physical_attempt_budget, prepared_lease_cold_setup_precedes_the_physical_attempt_budget, and public_protected_fenced_activation_prewarms_default_width_before_first_dispatch. Applying this conflicting older branch would revisit superseded fixture shapes rather than deliver a missing production prewarm implementation.

The branch and old failed-check evidence remain preserved. Any remaining latency or authority defect should be handled against the current main implementation; this closure does not assert that the old failing checks passed.