refactor(db): modular lib/ architecture and expanded test coverage

[unclecatvn]

Summary

• Refactor @unclecat/mcp-multi-db into focused lib/ modules: toolDescriptors, tableListingSql, normalizeAlias, aliasConstants, instructions, logger — toolHandlers.js shrinks ~480 → ~215 lines.
• Hoist shared driver logic into BaseDriver (listTables, healthCheck, error mapping); dialect drivers only implement executeQuery + describeTable.
• Add optional defaultAlias (omit databaseAlias in tool calls), per-alias defaultSchema, and db_list_tables pagination/filter (limit, offset, namePattern).
• Harden security: modeEnforcer gates on effectiveType so EXPLAIN ANALYZE <write> cannot bypass readonly mode.
• Expand tests to 203 with full lib/ + drivers/ coverage gate (≥88% lines).

Toolchain / CI cleanup

• Fix eslint: drop unused DEFAULT_PORTS import, use const in normalizeAlias.
• Apply prettier formatting to config.js, configFile.js, toolDescriptors.js.
• Bump vitest & @vitest/coverage-v8 to ^3.2.6 (db + odoo) — clears the critical vitest advisory.
• Add pnpm overrides forcing vite >=6.4.3 and esbuild >=0.28.1 — clears the remaining high advisories. pnpm audit --audit-level=high now passes (0 critical / 0 high).

Includes changeset .changeset/db-refactor-modular.md (minor bump). Pending .changeset/vscode-docs.md on staging/master will aggregate into the same Version Packages PR.

Test plan

• pnpm --filter @unclecat/mcp-multi-db test — 203/203 pass
• pnpm --filter @unclecat/mcp-multi-db test:coverage — ≥80% thresholds pass
• pnpm --filter @unclecat/mcp-odoo test — 94/94 pass
• Live MCP smoke test against unleashed alias (connection, query orders, list tables)
• CI ci-success green on PR
• After merge to master: verify Version Packages PR picks up both changesets