fix(scim): repair existing durable schemas

[thrashr888]

Summary

• add immutable forward migration 12 to restore SCIM tables and indexes skipped by existing databases
• reproduce the exact shipped legacy state while preserving unrelated durable data
• verify restart idempotence and the production SCIM startup path
• close agentkernel-snfo in the same substantive change

Validation

• cargo fmt -- --check
• git diff --check
• cargo test durable_storage::tests -- --nocapture
• cargo test --bin agentkernel scim::tests -- --nocapture
• cargo test --bin agentkernel scim_store_opens_after_legacy_schema_repair -- --nocapture
• cargo test --no-default-features --lib (299 passed, 2 ignored)
• cargo clippy -- -D warnings -A clippy::result_large_err
• cargo clippy --no-default-features -- -D warnings -A clippy::result_large_err

Note: all-target Clippy still reports unrelated pre-existing warnings in benchmark/example test targets on main.