feat(comfy): workflow validation and automated repair engine (M10)

[BerryUIKI]

Summary

This PR implements Milestone M10: Agent-Assisted Construction, Validation, Repair, and Execution of ComfyUI Workflows.

Key Capabilities

• ComfyUI DAG Syntax & Port Validation (\WorkflowValidator):
  • Full topological analysis verifying directed graph structure and checking for cycles via DFS.
  • Strict type checking across standard ComfyUI ports (\MODEL, \CLIP, \VAE, \LATENT, \IMAGE, \CONDITIONING, \UPSCALE_MODEL).
  • Detection of missing required inputs, broken link references (targeting non-existent node IDs), and missing indexed checkpoint dependencies.
• Automated Workflow Repair Engine (\WorkflowRepairer):
  • Deterministic heuristics to automatically reconnect missing VAE, CLIP, and MODEL slots using available sources in the graph.
  • Checkpoint dependency resolver substituting missing models with verified indexed local checkpoints.
  • Re-evaluates repaired graph to guarantee structural validity before execution.
• REST Endpoints & Agent Conversational Diagnostics:
  • \POST /api/v1/workflow/validate: Returns comprehensive \WorkflowValidationReport.
  • \POST /api/v1/workflow/repair: Returns repaired graph, applied \RepairAction\ list, and remaining issues.
  • Agent chat integration providing diagnostics and repair guidance.

Automated Verification

• Backend pytest: 95 passed (including 6 new tests in \�ackend/tests/test_m10_workflow_repair.py)
• Frontend: TypeScript typecheck and Vite build passed cleanly
• Launcher: \cargo test\ passed cleanly