[Phase 12] Add conflict detection and recovery UX

[cosentinode]

Goal

Make merge/rebase conflict states understandable and recoverable.

Scope

• Detect merge and rebase in-progress states.
• Show conflicted files prominently.
• Provide next-step actions: continue, abort, skip where applicable.
• Show conflict-related status in the main viewport.
• Prevent unrelated risky operations while conflict resolution is active.

Non-negotiables

• Code simplicity is a must: support the core conflict flows before advanced tooling.
• Security is a must: abort/continue operations must require explicit user intent.
• Scalability is a must: conflict state should be part of the repository model, not scattered UI checks.

Acceptance Criteria

• Merge conflicts are detected and displayed.
• Rebase conflicts are detected and displayed.
• Continue/abort actions call typed operations and are audited.