feat: conditional hotspot drag-to-connect and per-branch actions

[trmquang93]

Summary

• Drag-to-connect conditional branching from hotspots: Dragging from a hotspot with an existing connection to a new screen auto-converts to a conditional group. Additional drags add more branches. Duplicate targets are ignored.
• Per-branch action types: Each condition branch in the HotspotModal now has its own action dropdown (Navigate, Back, Modal, API Call, Custom) with full follow-up configuration including API endpoint/method/schema and success/error paths.
• Backward compatibility: importFlow.js backfills new condition branch fields for older .drawd files.

Files changed (9)

• src/hooks/useScreenManager.js — hotspotId params on convertToConditionalGroup/addToConditionalGroup + per-branch connection creation in saveHotspot()
• src/hooks/useInteractionCallbacks.js — Drag-to-conditional detection logic in onConnectComplete()
• src/Drawd.jsx — Wire convertToConditionalGroup to callbacks
• src/components/HotspotModal.jsx — Per-branch action UI with action dropdown, target/dataflow, API fields, success/error follow-ups
• src/utils/instructionRenderers.js — Per-branch action rendering in generated instructions
• src/utils/importFlow.js — Backfill new condition branch fields
• mcp-server/src/tools/hotspot-tools.js — Updated conditions schema with per-branch action fields
• mcp-server/src/state.js — Per-branch connection creation for MCP
• src/pages/docs/userGuide.md — Documentation for new features

Test plan

• Drag from hotspot to Screen A (single navigate connection)
• Drag from same hotspot to Screen B (auto-converts to conditional, inline labels appear)
• Drag from same hotspot to Screen C (third branch added)
• Drag to Screen A again (ignored as duplicate)
• Undo reverts to single connection
• HotspotModal: set action=conditional, verify each branch has action dropdown with all 5 types
• Test API branch with endpoint, method, success/error follow-ups
• Save and verify correct connections created per branch action
• Load old .drawd file with conditions — verify backfill works
• Screen-to-screen conditional still works (regression)