Fix Blend adapter admin retargeting

[carrion256]

Summary

• remove the undeployed Blend adapter set_pool and set_vault admin retarget entrypoints
• delete stale pool_upd / vlt_upd event surface and obsolete setter tests
• remove justfile recipes that invoked the deleted retarget methods
• add a source-shape regression that fails if the public retarget ABI/events return

Nexus

• 81068879-6d1a-460a-b176-bc982fb254cd

Verification

• RED before fix: cargo test -p templar-soroban-blend-adapter blend_adapter_does_not_expose_admin_retarget_entrypoints -- --nocapture failed on pub fn set_pool
• GREEN: cargo fmt --all -- --check
• GREEN: git diff --check
• GREEN: cargo test -p templar-soroban-blend-adapter -- --nocapture (12 unit + 7 integration passed)
• GREEN: cargo test -p templar-soroban-runtime --features testutils --lib -- --nocapture (103 passed)
• GREEN: cargo test -p templar-soroban-runtime --features testutils --test property_tests -- --nocapture (23 passed)
• GREEN: just -f contract/vault/soroban/justfile size-budget-check (93961 <= 131072)
• GREEN: source sweep zero matches for Blend adapter retarget methods/events; justfile listing no longer advertises blend-adapter-set-pool / blend-adapter-set-vault

Notes

Contracts are undeployed, so this PR removes the mutable retargeting ABI instead of adding a timelock wrapper around it.

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[carrion256]

Superseded by #431, which consolidates the tracker-defined adapter-accounting-and-blend-admin boundary for A-032/A-033/A-034/A-035/A-060. Closing this split draft so auditors have one adapter follow-up PR to review.

[carrion256]

Closed as superseded by #431 consolidated adapter-accounting-and-blend-admin PR.