feat: scaffold backend command boundary and app state container (issue #15)

[thundermiracle]

Summary

• implement modular Rust backend structure for Issue P0-BASE: Define backend command boundary and application state container #15: commands, contracts, and state
• add centralized AppState container with deterministic lifecycle snapshot and operation ID generation
• add Tauri command boundary placeholders: detect_clients, list_resources, mutate_resource
• standardize shared backend envelope contract (ok, data, error, meta) and typed request/response models
• add frontend typed invoke layer in src/backend/ and update UI to call all three placeholder commands
• introduce Biome-based TS/JS lint pipeline (lint:ts) and add biome.json
• add unit tests for command boundary contracts and state behavior

Commit Structure

• feat(rust): scaffold command boundary and app state container (issue #15)
• feat(ts): add typed invoke client and biome lint pipeline (issue #15)

Validation

• pnpm outdated
• pnpm run lint
• pnpm test
• cargo test --manifest-path src-tauri/Cargo.toml

Closes #15