docs: correct lint, format, and test commands in AGENTS.md and development.md

Replace outdated ESLint/Prettier/npm references with actual toolchain:
deno lint, deno fmt, deno install, cargo nextest. Add dedicated
"Linting, Formatting, and Testing" section to AGENTS.md with both
Task runner and direct commands.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pythoninthegrass

AGENTS.md

@@ -72,6 +72,47 @@ The queue store (`app/frontend/js/stores/queue.js`) maintains tracks in **play o
 
 **Now Playing view**: Always displays tracks in the order they will play (current track first, then upcoming).
 
+## Linting, Formatting, and Testing
+
+All commands use Taskfile. Run `task --list` for full list.
+
+### Task Runner (preferred)
+
+```bash
+task lint                     # Run all linters (Rust + JS)
+task format                   # Run all formatters (Rust + JS)
+task test                     # Run all tests (Rust + JS unit)
+task test:e2e                 # Run Playwright E2E tests
+task pre-commit               # Run pre-commit hooks
+```
+
+### Direct Commands
+
+**Frontend** (uses Deno toolchain, not ESLint/Prettier):
+
+```bash
+deno lint                                         # Lint JS/TS
+deno fmt                                          # Format JS/TS
+deno fmt --check                                  # Check formatting without changes
+cd app/frontend && npx vitest run                 # Unit/property tests (Vitest via Node)
+cd app/frontend && npx playwright test            # E2E tests
+```
+
+**Backend** (Rust):
+
+```bash
+cargo clippy --workspace                          # Lint
+cargo fmt --all                                   # Format
+cargo nextest run --workspace                     # Tests (falls back to cargo test)
+cargo check --manifest-path src-tauri/Cargo.toml  # Fast type check (no binary)
+```
+
+### When to Run
+
+- **Before committing**: `task lint && task format`
+- **After changing frontend code**: `cd app/frontend && npx vitest run`
+- **After changing Rust code**: `cargo nextest run --workspace`
+
 ## Implementation Notes
 
 1. **Components**: Modular, single-responsibility. Use Alpine.js for interactivity, basecoat/Tailwind for styling.

deno.lock

@@ -78,25 +78,26 @@ When running `task build`, the following happens automatically:
 
 ```bash
 # Install dependencies
-npm install                           # Frontend dependencies
-cargo build                           # Rust backend dependencies
+deno install --node-modules-dir=auto --frozen  # Frontend (8x faster than npm ci)
+cargo build                                    # Rust backend
 
 # Fast syntax/type checking (no binary output, 2-3x faster than build)
 cargo check --manifest-path src-tauri/Cargo.toml
 cargo check --all-features
 
 # Linting
-npm run lint                          # Frontend (ESLint)
-cargo clippy                          # Rust
+deno lint                             # Frontend (Deno linter)
+cargo clippy --workspace              # Rust
 
 # Formatting
-npm run format                        # Frontend (Prettier)
-cargo fmt                             # Rust
-
-# Tests directly
-cargo test --manifest-path src-tauri/Cargo.toml  # Rust backend
-npm --prefix app/frontend test                    # Vitest unit
-npm --prefix app/frontend run test:e2e            # Playwright E2E
+deno fmt                              # Frontend (Deno formatter)
+deno fmt --check                      # Check without changes
+cargo fmt --all                       # Rust
+
+# Tests
+cargo nextest run --workspace                   # Rust (falls back to cargo test)
+cd app/frontend && npx vitest run               # Vitest unit/property tests
+cd app/frontend && npx playwright test          # Playwright E2E
 
 # Pre-commit hooks
 pre-commit run --all-files