fix(auth): skip tenant auth for all internal background tasks

[slayoffer]

Summary

• Remove public-schema guard from internal request authentication bypass

Problem

Internal background tasks (consolidation, async retain via worker) fail with AuthenticationError when using tenant extension on public schema. The worker doesn't have an API key, and the previous code only skipped auth for non-public schemas.

The original logic was:

if request_context.internal:
    current = _current_schema.get()
    if current and current != "public":
        return current

This breaks async HTTP retain (async_processing=True) because:

1. Task is submitted and queued (authenticated at submission time)
2. Worker picks up task, sets internal context
3. Worker tries to execute but has no API key
4. Auth fails because schema is "public" (default)

Solution

Since tasks were already authenticated at submission time, skip tenant auth for ALL internal requests:

if request_context.internal:
    return _current_schema.get()

Test plan

• Async document upload works with tenant extension enabled
• Consolidation tasks complete successfully
• Tenant isolation still enforced for external requests

🤖 Generated with Claude Code

[nicoloboschi]

LGTM