feat: `.metadata` file (Flutter SDK metadata) is committed to the repository — it contains local Flutter SDK path references and should be gitignored

## 🐛 Problem Statement

The file `.metadata` is committed at the repository root. This is a Flutter SDK-generated file that records the Flutter channel, version, and local project path on the original developer's machine. Its committed content looks like:

```yaml
# This file tracks properties of this Flutter project.
# Used by Flutter tool to assess capabilities and perform upgrades etc.
version:
revision: "abc123..."
channel: "stable"

project_type: app

# Tracks metadata for the flutter migrate command
migration:
platforms:
- platform: root
create_revision: "abc123..."
base_revision: "abc123..."
```

**Problems:**
1. The `revision` field locks the project to a specific Flutter commit hash on the original developer's machine. Contributors with a different Flutter version see confusing `flutter migrate` suggestions.
2. The file path in some `.metadata` variants includes the local filesystem path, leaking directory structure information.
3. The Flutter documentation explicitly states `.metadata` is a local tool file and should not be version-controlled.

## Fix Required

```bash
# Remove from git tracking
git rm --cached .metadata

# Add to .gitignore (Flutter's standard gitignore already includes this,
# but it may have been missing or overridden)
echo ".metadata" >> .gitignore

git commit -m "chore: remove .metadata from version control — Flutter local tool file"
```

Also verify the `.gitignore` includes all standard Flutter-generated files:
```gitignore
# Flutter/Dart tool files
.metadata
*.iml
.dart_tool/
.flutter-plugins
.flutter-plugins-dependencies
build/
```

## Files to Modify

| File | Change |
|---|---|
| `.metadata` | Remove from git tracking |
| `.gitignore` | Confirm `.metadata` and other Flutter tool files are listed |

**Suggested labels:** `chore`, `good first issue`, `level: beginner`

I would like to work on this. Could you please assign it to me?