Fix active no-signal drain budget continuations

[chubes4]

Summary

• Add explicit active/no-signal drain continuations when the budget expires before the next safe stage or after a bounded cleanup pass.
• Return a clear continuation reason, hint, stage, offset, and next command instead of falling through to finalization.
• Cover budget-boundary continuation behavior in the abandoned cleanup orchestrator smoke test.

Closes #823

Tests

• php -l inc/Workspace/WorkspaceAbandonedCleanupOrchestrator.php
• php -l tests/smoke-abandoned-cleanup-orchestrator.php
• php tests/smoke-abandoned-cleanup-orchestrator.php
• php tests/workspace-compact-output.php
• php tests/smoke-cleanup-eligible-drain.php
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 and OpenCode
• Used for: Implementing the active/no-signal drain budget-continuation fix, updating focused smoke coverage, and running verification.