chore: add mise format and lint tasks (ruff + Biome)

Tools are pinned in mise.toml. ruff.toml points first-party detection at backend/, since the frontend's src/auth, src/books and src/notes otherwise get matched as first-party. biome.json uses spaces to match the existing Prettier-style formatting. Also combines a nested with in test_passwords.py (ruff SIM117).

mise.toml

@@ -1,10 +1,11 @@
 [tools]
 python = "3.14"
 node = "24"
+ruff = "0.16.10"
+biome = "2.5.15"
 
 [tasks.setup]
 description = "Create the venv and install backend and frontend dependencies"
-# ponytail: reinstalls on every run (fast when up to date); add sources/outputs if it ever gets slow
 run = [
   "python -m venv .venv",
   ".venv/bin/pip install -q --disable-pip-version-check -r backend/requirements.txt",
@@ -31,3 +32,27 @@ run = "npm run dev"
 [tasks.dev]
 description = "Start the app for local testing (API + UI)"
 depends = ["dev:api", "dev:web"]
+
+[tasks."format:py"]
+description = "Sort imports and format the backend"
+run = ["ruff check --select I --fix backend", "ruff format backend"]
+
+[tasks."format:ts"]
+description = "Sort imports and format the frontend"
+run = "biome check --write --linter-enabled=false src vite.config.ts"
+
+[tasks.format]
+description = "Format and auto-fix Python and TypeScript"
+depends = ["format:py", "format:ts"]
+
+[tasks."lint:py"]
+description = "Lint the backend and verify formatting (no writes)"
+run = ["ruff check backend", "ruff format --check backend"]
+
+[tasks."lint:ts"]
+description = "Lint the frontend and verify formatting (no writes)"
+run = "biome check src vite.config.ts"
+
+[tasks.lint]
+description = "Lint and format-check Python and TypeScript (CI-safe, no writes)"
+depends = ["lint:py", "lint:ts"]