Consolidate thread runtime state and use typed UI snapshots

[VolkerChristian]

Summary

• consolidate per-thread hydration, settings, dispatch, resume, and recovery bookkeeping into one ThreadRuntimeState record
• preserve narrow reconnect, reload, and thread-removal semantics while eliminating synchronized parallel-container cleanup
• replace synthetic JSON and serialized fingerprints with typed optional snapshots in Shell, ThreadPane, and Inspector rendering
• compare GitDiffSnapshot values directly instead of allocating a byte buffer and calculating SHA-256
• refresh request thread labels after renames and Git presentation after metadata-only changes
• top-align rich-text subagent results so surplus label height does not create a large blank gap

Regression coverage

• request cards update their displayed thread title after thread.name.changed
• Git Changes updates when only previously omitted additions and deletions metadata changes
• agent Markdown result labels remain top-aligned

Validation

• focused Application Layout, Shell Integration, and Git Changes Live checks passed
• complete CTest suite: 7/7 passed
• git diff --check passed

Scope

This remains a behavior-preserving ownership and type-safety cleanup. It adds no controllers, caches, repositories, event systems, or protocol-authority changes. HistoryWindow and PromptCoordinator ownership remain unchanged.