fix: support remote template preview and export

[andrei-hasna]

Summary

• route template-preview and template-export through authenticated self-hosted /v1/templates/:id reads
• preserve local canonical preview and export/import shapes without SQLite fallback
• cover cloud preview, export, export-to-import round-trip, conditions, empty-description normalization, and remote entrypoint isolation

Validation

• bun run typecheck
• bun test src/cli/cloud-list-filter.test.ts
• bun test src/cli/remote-entrypoint.test.ts
• bun run build:server
• staged and commit-range gitleaks scans