feat: Phase 5 — Holographic Core (payload system, rules, HUD, worker, spring drag, tests)

[akaradje]

Summary

Implements the remaining blueprint features for the Liquid-State Engine:

• Data Payload System — Opaque payloads (text/number/json/array) attached to each physics node via a JS-side registry. Wasm emits a packed u32 event queue for spawn/despawn/merge/fracture.
• Generic Rule Engine — Pure JS functions for per-type merge and fracture semantics. Configurable numeric reducer (sum/avg/product). Auto-detect payload type from raw input.
• Draw Mode & Drag-and-Drop — Mouse-drag path tracing creates new nodes; file/text drop onto canvas creates payload nodes; payload dialog for labeling.
• Glassmorphism HUD — Preact+htm via CDN (no build step). Mode switcher, floating inspector, physics config toolbar, translucent blurred panels.
• Web Worker — Wasm engine runs in background thread. SharedArrayBuffer + Atomics path with COOP/COEP headers; transfer-based postMessage fallback.
• Spring-Damped Drag — Hooke's law spring + velocity damping replaces brute-force drag. pin_node/unpin_node/update_pin_target API.
• Tests & Examples — 12 Rust unit tests (ECS round-trip, quadtree query, bitwise merge/fracture). Example page for JSON/number/text data workflows.

Files Changed

18 files, +2617 / -309 lines

Verification Checklist

• cargo check --target wasm32-unknown-unknown — clean, no warnings
• cargo test — 12/12 tests pass
• All existing Wasm APIs preserved
• HUD renders above canvas, pointer-events selectively enabled
• No DOM inside canvas — all node visuals remain pixel-rendered by Rust
• SoA memory layout maintained
• Dirty rectangle strategy unchanged
• Worker path degrades gracefully: SAB → transfer → single-threaded

How to Test

npm run build:wasm
npm run serve
# Open http://localhost:8080/web/
# Open http://localhost:8080/examples/data-workflow.html

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