fix: scope chat run control by workspace

[chubes4]

Summary

• validate and thread canonical workspace through chat dispatch, run status/events/cancel, queue claims, and conversation-loop cancellation
• add an optional workspace-aware run-control store capability, with explicit workspace state isolated in network options while omitted workspace remains site-local
• bind stored runs and queued messages to conversation-owner fingerprints and fail unsupported stores explicitly

Tests

• composer test
• composer phpstan
• PHP syntax checks for all changed PHP files
• homeboy review audit --placement local --profile pr --changed-since origin/main --json-summary (no introduced findings)
• homeboy review lint --placement local --changed-only --summary attempted; Homeboy's bundled PHPCS installation fatals because PHP_CodeSniffer\\Reports\\Report is missing, and its bundled PHPStan is also corrupted. Repository PHPStan passes independently.

Fixes #449