fix: preserve composite indexes in generated SQL

[snvtac]

This PR preserves composite indexes when generating table SQL from index metadata.

Changes

• Added seq_in_index to the frontend Index metadata type.
• Grouped index metadata rows by index name before rendering CREATE INDEX statements.
• Ordered grouped columns by seq_in_index, falling back to input order when sequence data is unavailable.
• Added regression coverage for composite non-unique indexes, composite unique indexes, sequence ordering, and table-level generated SQL output.

Validation

• pnpm exec vitest run tests/utils/sqlGenerator.test.ts — 64 passed
• pnpm typecheck
• pnpm lint — passes with one existing SettingsProvider.tsx hook dependency warning
• pnpm build — passes with an existing Vite dynamic/static import chunking warning

Closes #349

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (3 files)

• src/types/schema.ts
• src/utils/sqlGenerator.ts
• tests/utils/sqlGenerator.test.ts

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_{Reviewed by kimi-k2.6-20260420 · Input: 61.9K · Output: 6.2K · Cached: 314.6K}