refactor: simplify large temper-server modules

[nerdsane]

Summary

• split the largest temper-server evolution and WASM modules into focused submodules so the top-level files only coordinate flow
• dedupe repeated OData entity-loading/query-application paths while preserving the existing select/expand ordering differences
• move refactor-local tests into dedicated module test files so the production files are smaller and easier to navigate

Readability impact

• PROD_FILES_GT1000: 3 -> 0
• PROD_MAX_FILE_LINES: 1823 -> 938
• largest production file moved out of temper-server; max is now crates/temper-store-turso/src/router.rs
• readability advisory remains PROD_FILES_GT300: 108 -> 112

Verification

• cargo fmt --all --check
• cargo test -p temper-server --features observe
• pre-push verification pipeline
• cargo clippy --workspace --all-targets --all-features -- -D warnings (via pre-push gate)
• bash scripts/readability-ratchet.sh check .ci/readability-baseline.env (via pre-push gate)
• full workspace test suite including deterministic simulation suites and doctests (via pre-push gate)