chore: rewrite justfile for pyenv + poetry dev workflow 🔧

Replaces outdated PyInstaller-only recipe with full task runner:
install, test, coverage, coverage-html, test-one, fmt, fmt-check, ci, run,
build, clean. PATH export wires in pyenv shims and poetry automatically.

justfile

@@ -1,17 +1,96 @@
 #!/usr/bin/env just --justfile
+# directdnsonly — developer task runner
+# Requires: just, pyenv, poetry
+
 APP_NAME := "directdnsonly"
+
+# Ensure pyenv shims and common install locations are on PATH so that `python`
+# resolves via pyenv (.python-version) and `poetry` is found without a full
+# shell init in every recipe.
+export PATH := env_var("HOME") + "/.pyenv/shims:" + env_var("HOME") + "/.pyenv/bin:" + env_var("HOME") + "/.local/bin:" + env_var("PATH")
+
+# List available recipes (default)
+default:
+    @just --list
+
+# ---------------------------------------------------------------------------
+# Setup
+# ---------------------------------------------------------------------------
+
+# Install all dependencies (including dev group)
+install:
+    poetry install
+
+# Install only production dependencies
+install-prod:
+    poetry install --only main
+
+# Show the Python interpreter that will be used
+which-python:
+    @poetry run python --version
+    @poetry run python -c "import sys; print(sys.executable)"
+
+# ---------------------------------------------------------------------------
+# Testing
+# ---------------------------------------------------------------------------
+
+# Run the full test suite
+test:
+    poetry run pytest tests/ -v
+
+# Run tests with terminal coverage report
+coverage:
+    poetry run pytest tests/ -v --cov=directdnsonly --cov-report=term-missing
+
+# Run tests with HTML coverage report (opens in browser)
+coverage-html:
+    poetry run pytest tests/ --cov=directdnsonly --cov-report=html
+    @echo "Coverage report: htmlcov/index.html"
+
+# Run a single test file or pattern, e.g. just test-one test_reconciler
+test-one target:
+    poetry run pytest tests/ -v -k "{{target}}"
+
+# ---------------------------------------------------------------------------
+# Code quality
+# ---------------------------------------------------------------------------
+
+# Format all source and test files with black
+fmt:
+    poetry run black directdnsonly/ tests/
+
+# Check formatting without making changes (CI-safe)
+fmt-check:
+    poetry run black --check directdnsonly/ tests/
+
+# CI gate — run fmt-check then test, fail fast
+ci: fmt-check test
+
+# Start the application
+run:
+    poetry run python -m directdnsonly
+
+# ---------------------------------------------------------------------------
+# Build
+# ---------------------------------------------------------------------------
+
+# Build a standalone binary with PyInstaller
 build:
-    cd src && \
-    pyinstaller \
-    -p . \
+    poetry run pyinstaller \
         --hidden-import=json \
-    --hidden-import=pyopenssl \
         --hidden-import=pymysql \
-    --hidden-import=jaraco \
         --hidden-import=cheroot \
         --hidden-import=cheroot.ssl.pyopenssl \
         --hidden-import=cheroot.ssl.builtin \
-    --hidden-import=lib \
-    --hidden-import=os \
-    --hidden-import=builtins \
-    --noconfirm --onefile {{APP_NAME}}.py
+        --noconfirm --onefile \
+        directdnsonly/main.py
+
+# ---------------------------------------------------------------------------
+# Clean
+# ---------------------------------------------------------------------------
+
+# Remove build artefacts, caches, and compiled bytecode
+clean:
+    rm -rf dist/ build/*.spec .coverage htmlcov/ .pytest_cache/
+    find . -type d -name __pycache__ -exec rm -rf {} + 2>/dev/null || true
+    find . -name "*.pyc" -delete 2>/dev/null || true