test(clickhouse): auto-discover migrations in bundled_migrations() smoke test

[eric-tramel]

Summary

• Replaces the hard-coded assert_eq!(migrations.len(), N) in bundled_migrations_registers_all_sql_files with a directory walk of sql/ that diffs discovered filenames against the names returned by bundled_migrations().
• Adds two ordering invariants: bundled_migrations() must be sorted ascending by version, and each entry's name must start with its version's numeric prefix.
• Fixes the silent false-green regression that hit twice — #221 (migration 011) and #230 (migration 012) — where a new sql/NNN_*.sql was added without a matching include_str! entry but the count-based test still passed because N was not bumped.

Closes #233.

How the new check works

1. std::fs::read_dir($CARGO_MANIFEST_DIR/../../sql) enumerates every file matching ^\d{3}_.+\.sql$.
2. Result is sorted and compared against bundled_migrations().iter().map(|m| m.name) — assertion failure prints both lists with a diff, so missing/extra entries are immediately visible.
3. Separate unit test pins the filename matcher's behavior (01_foo.sql, 0001_foo.sql, README.md, etc. are rejected; 001_foo.sql is accepted).

A file registered in bundled_migrations() but missing from disk is already caught at compile time by include_str!, so no runtime check is needed for that direction.

Verification

• cargo test -p moraine-clickhouse --lib — 12 passed.
• Manually added a stub sql/099_fake_unregistered.sql and reran the test: it now fails with the full filename diff pointing at the unregistered file, then cleaned up.
• cargo clippy --workspace --all-targets --locked -- -Dwarnings (strict baseline) — clean.

Test plan

• New test passes on main as-is.
• New test fails loudly when a sql/NNN_*.sql is added without a matching bundled_migrations() entry.
• Filename matcher correctly rejects non-conforming names (covered by dedicated unit test).
• cargo fmt --all -- --check clean.
• cargo clippy strict baseline clean.

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