refactor: use git-warp API properly — eliminate pass-through wrappers

[flyingrobots]

Summary

git-mind wraps @git-stunts/git-warp in thin abstraction layers that obscure the real API and duplicate capabilities the graph engine already provides. This issue tracks eliminating unnecessary wrappers and replacing hand-rolled logic with native WARP APIs.

Phases

• Phase 1: Kill pass-through wrappers (getNodes, hasNode, saveGraph, loadGraph)
• Phase 2: Replace thin wrappers with native API (getNodesByPrefix, queryEdges, getNode)
• Phase 3: Use query API in views
• Phase 4: Use graph.patch() convenience API
• Phase 5: Content — verify native API alignment
• Phase 6: Evaluate dag.js vs graph.traverse

Motivation

• Reduce indirection and make the codebase speak git-warp fluently
• Remove dead code (saveGraph has zero call sites)
• Eliminate ~60 call site updates of wrapper functions that add zero value