feat: minimal grocery list — add items, check them off

- Groceries DB schema (id, name, checked, created_at) with Drizzle + libsql
- /+page.server.ts: load (unchecked items, newest first), add & toggle actions
- /+page.svelte: text input + Add button, item list with toggle buttons
- Mobile-first styling with scoped CSS classes
- AGENTS.md: project-specific rules including UI validation

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+## Engineering Principles
+
+- Never delete published software versions
+- Never run sudo commands yourself, ask the user
+- Use `lightpanda` when internet access is needed; run `lightpanda --help` first to get the full list of available commands and options
+- Surface assumptions before building. Wrong assumptions held silently are the most common failure mode.
+- Push back when warranted. The agent (or engineer) is not a yes-machine.
+- Prefer the boring, obvious solution. Cleverness is expensive.
+- Touch only what you're asked to touch.
+- When scripting is necessary, create a python file, use inline metadata for dependencies and `uv run <script.py>`
+- Stop and ask when requirements conflict. Don't guess.
+- Ask if it works before commiting
+- All code comments must be in English. No French comments in code.
+
+## Implementation
+
+- Add a few logs at the feature level (not inside every unit function).
+- When possible, start with a failing test and ask for user validation before implementing the fix or feature.
+- No new tests are needed during pure refactoring.
+
+## Software Design
+
+- Ubiquitous Language - Names matter. Ask the user when defining a new concept
+- Entity - Objects having a stable identity encapsulate data and invariants
+- Value Objects - Immutable, self-validating. Date, Money, ...
+- Enum-to-enum conversion - Never convert one enum to another with a ternary or `if/else`. A ternary silently collapses every unhandled input value into the fallback branch, so adding a new member to the source enum compiles without error and produces a wrong result. Use an exhaustive object map typed as `Record<SourceEnum, TargetEnum>` so a new source member is a compile error until it is mapped.
+
+## Tools
+
+- Toujours utiliser `rg` (ripgrep) à la place de `grep` pour la recherche dans les fichiers
+- Toujours utiliser `find` pour la recherche de fichiers par nom/chemin
+
+## Feature Completion
+
+Avant de considérer une feature comme terminée, toujours exécuter dans l'ordre :
+
+1. Formatage du code
+2. Lint (`pnpm lint` ou équivalent)
+3. Build (`pnpm build` ou équivalent)
+4. Tests (`pnpm test` ou équivalent sur le scope impacté)
+
+## Testing
+
+- Utiliser des UUID plutôt que des 'machin-id' dans les tests
+
+## Dependency Changes
+
+- Ne pas edit les dépendances manuellement, utiliser le package manager
+
+1. Edit all config files in one pass
+2. Run `pnpm install --lockfile-only` to update lockfile
+3. Run `pnpm why <package>` to verify removal
+4. Run tests to confirm nothing broke
+
+## Documentation
+
+- After finishing a new feature, add a one line entry to the README explaining the feature for a user.
+
+## Data
+
+Filling CSV may be easier using cat to append a line at the end, than to edit the file.
+You can add data at the end, and sort it later if needed.
+
+## UI Validation
+
+- Always validate the UI visually before finishing a task (fetch the page via
+  lightpanda or check the rendered HTML/CSS output to verify layout is
+  correct).