Add external data replication plugin

[mdp28]

/claim #72

Summary

• Adds a ReplicationPlugin that pulls configured external tables into the internal StarbaseDB Durable Object SQLite database.
• Supports selected columns, static where clauses, cursor-based incremental sync, configurable batch size/interval, upsert/replace/insert modes, table-specific manual pulls, and a status endpoint.
• Persists per-table cursor/run state in internal tmp_starbasedb_replication_* tables.
• Exports the plugin from @outerbase/starbasedb/plugins and documents usage in plugins/replication/README.md.
• Fixes plugin beforeQuery chaining so a plugin hook runs once per plugin while preserving chained SQL/params.

Verification

• corepack pnpm install --frozen-lockfile --ignore-scripts
• corepack pnpm exec vitest run plugins/replication/index.test.ts src/plugin.test.ts
• git diff --check

Targeted test result: 2 files passed, 14 tests passed.