Move inline template strings from cli.ts into separate .tpl files under
src/templates/ for readability and maintainability. Update xrpc template
with $hatk import and typed query results. Include viewer handle in
ScopeMissing and proxy error responses so the generated client can
preserve identity across re-authentication redirects.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Wraps existing pds-proxy functions so hooks and XRPC handlers can write
records through the PDS with local indexing, without raw SQL. Also adds
awaitBackfill so ensureRepo properly waits for in-flight backfills.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>