feat: implement contract graph → Soroban WASM compilation pipeline

[GideonBature]

Summary

Implements the core compilation pipeline for LumensBlock: visual block graphs are validated, converted to Soroban Rust source, compiled to WASM via cargo, and wired into the deploy flow.

Changes

• ContractGraph schema — TypeScript types and JSON Schema for nodes, edges, block parameters, and compile errors (frontend/src/lib/compile/)
• Validation — Rejects malformed, oversized, or structurally invalid graphs with structured { code, message } errors
• Codegen — BFS traversal from Start generates Soroban contract source for Auth, Transfer, Storage, Event, and Condition blocks
• Compiler — Temp crate + cargo build --target wasm32-unknown-unknown --release wrapper
• POST /api/compile — Accepts a graph, returns base64 WASM or a compilation error
• Deploy integration — deployContract() calls the compile endpoint; DeployButton surfaces human-readable errors
• Tests — Vitest unit tests for validation and codegen; CI runs npm test
• Editor fixes — Resolves merge conflicts in BlockEditor.tsx and Toolbar.tsx

Approach

Server-side codegen (graph JSON → generated Rust → WASM) rather than pre-compiled templates, for flexibility as block types grow.

Test plan

• npm test — validation and codegen unit tests pass
• npx tsc --noEmit — type-check passes
• Load Token Transfer template → Deploy → compiles and shows WASM summary
• Invalid graph (Start only) → structured error shown in UI
• Oversized/malformed payload → API returns 400 with readable message
• Requires Rust + wasm32-unknown-unknown for full WASM compilation locally

Closes #3.