feat(db): add catalog inspection and explain

[sanohiro]

Summary

• complete the D12 common and driver-native SQLite/PostgreSQL catalog inspection surfaces;
• add common/native generic EXPLAIN lowering, exact option and validation precedence, explicit-region results, and native cursor cleanup;
• add whole-program, per-unit, malformed-native-result, SQLite runtime, and required PostgreSQL integration owners;
• synchronize the English and Japanese pkg.db design records for the completed Q5b2 boundary.

This capability intentionally keeps catalog categories, native cursor ownership, EXPLAIN, and the compiler generic bridge in one PR. They form one read-only failure domain; splitting the producer/consumer chain would duplicate the ABI, allocation, cleanup, and validation proof without leaving a useful stable intermediate consumer.

Review fixes

• project PostgreSQL sort/null evidence only for B-tree index terms;
• seal root catalog adapters with controls constructible only under pkg.db.internal;
• enforce driver restriction before complete live-state validation in both native drivers.

Verification

• pkg_db_q5b2: 10 passed locally; the required live PostgreSQL execution is CI-owned and locally skipped without ALIGN_DB_POSTGRES_URL, while its full fixture type-check passed;
• focused Q5b1 materializer owner passed;
• cumulative library gate passed across all workspace crates; macOS stalled twice at _dyld_start while switching test binaries, so the completed phases were preserved and only the unfinished align_mir/parser/sema/span slices were continued;
• workspace lib/bin Clippy passed with -D warnings;
• git diff --check passed.