Add firebase-data-connect-basics skill (#7)

* Add firebase-data-connect-basics skill

* Add firebase dataconnect basic skills

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Co-authored-by: Muhammad Talha <muhammadtalhar@google.com>

Author: joehan

skills/firebase-data-connect-basics/SKILL.md

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+---
+name: firebase-data-connect
+description: Build and deploy Firebase Data Connect backends with PostgreSQL. Use for schema design, GraphQL queries/mutations, authorization, and SDK generation for web, Android, iOS, and Flutter apps.
+---
+
+# Firebase Data Connect
+
+Firebase Data Connect is a relational database service using Cloud SQL for PostgreSQL with GraphQL schema, auto-generated queries/mutations, and type-safe SDKs.
+
+## Quick Start
+
+```graphql
+# schema.gql - Define your data model
+type Movie @table {
+  id: UUID! @default(expr: "uuidV4()")
+  title: String!
+  releaseYear: Int
+  genre: String
+}
+
+# queries.gql - Define operations
+query ListMovies @auth(level: PUBLIC) {
+  movies { id title genre }
+}
+
+mutation CreateMovie($title: String!, $genre: String) @auth(level: USER) {
+  movie_insert(data: { title: $title, genre: $genre })
+}
+```
+
+## Project Structure
+
+```
+dataconnect/
+├── dataconnect.yaml      # Service configuration
+├── schema/
+│   └── schema.gql        # Data model (types with @table)
+└── connector/
+    ├── connector.yaml    # Connector config + SDK generation
+    ├── queries.gql       # Queries
+    └── mutations.gql     # Mutations
+```
+
+## Core Concepts
+
+| Concept | Description |
+|---------|-------------|
+| **Schema** | GraphQL types with `@table` → PostgreSQL tables |
+| **Connector** | Collection of queries/mutations as API endpoints |
+| **Generated Fields** | Auto-generated `movie`, `movies`, `movie_insert`, `movie_update`, `movie_delete` |
+| **Key Scalars** | `Movie_Key` type for record identification |
+| **@auth** | Authorization directive: `PUBLIC`, `USER`, `USER_EMAIL_VERIFIED`, `NO_ACCESS` |
+
+## Detailed References
+
+**Design your data model** → See [schema.md](reference/schema.md)
+- Types, @table, @col, @default directives
+- Relationships with @ref (one-to-one, one-to-many, many-to-many)
+- Data types: UUID, String, Int, Int64, Float, Boolean, Date, Timestamp, Vector
+
+**Build queries and mutations** → See [operations.md](reference/operations.md)
+- Generated fields and key scalars
+- Filtering with `where`, `orderBy`, `limit`
+- Relational queries with `_on_` and `_via_` syntax
+- Multi-step mutations with `@transaction`
+
+**Secure your operations** → See [security.md](reference/security.md)
+- @auth directive and access levels
+- CEL expressions for custom authorization
+- @check and @redact for data lookup authorization
+- Common authorization patterns and anti-patterns
+
+**Integrate with client apps** → See [sdks.md](reference/sdks.md)
+- Web, Android, iOS, Flutter SDK usage
+- SDK generation with Firebase CLI
+- Calling queries/mutations from client code
+
+**Configure and deploy** → See [config.md](reference/config.md)
+- dataconnect.yaml and connector.yaml structure
+- Firebase CLI commands
+- Local emulator setup
+- Deployment workflow
+
+**Advanced features** → See [advanced.md](reference/advanced.md)
+- Vector similarity search with Vertex AI embeddings
+- Full-text search with @searchable directive
+- Cloud Functions integration (mutation triggers)
+- Data seeding and bulk operations
+
+## Common Patterns
+
+### User-Owned Resources
+
+```graphql
+type Post @table {
+  id: UUID! @default(expr: "uuidV4()")
+  authorUid: String! @default(expr: "auth.uid")
+  content: String!
+}
+
+mutation CreatePost($content: String!) @auth(level: USER) {
+  post_insert(data: { authorUid_expr: "auth.uid", content: $content })
+}
+
+query MyPosts @auth(level: USER) {
+  posts(where: { authorUid: { eq_expr: "auth.uid" }}) { id content }
+}
+```
+
+### Many-to-Many Relationship
+
+```graphql
+type Movie @table {
+  id: UUID! @default(expr: "uuidV4()")
+  title: String!
+}
+
+type Actor @table {
+  id: UUID! @default(expr: "uuidV4()")
+  name: String!
+}
+
+type MovieActor @table(key: ["movie", "actor"]) {
+  movie: Movie!
+  actor: Actor!
+  role: String!
+}
+```
+
+### Filtered Queries
+
+```graphql
+query MoviesByGenre($genre: String!, $minRating: Int) @auth(level: PUBLIC) {
+  movies(
+    where: { genre: { eq: $genre }, rating: { ge: $minRating }},
+    orderBy: [{ rating: DESC }],
+    limit: 10
+  ) { id title rating }
+}
+```
+
+## Examples & Templates
+
+**Complete working examples** → See [examples.md](examples.md)
+**Ready-to-use templates** → See [templates.md](templates.md)
+
+## MCP Tools Available
+
+- `firebase_init` - Initialize Data Connect with `dataconnect` feature
+- `firebase_get_sdk_config` - Get Firebase configuration for client apps
+- `firebase_get_project` - Get current project information
+- `firebase_update_environment` - Set project directory and active project
+
+## CLI Commands
+
+```bash
+# Initialize Data Connect
+firebase init dataconnect
+
+# Start emulator for local development
+firebase emulators:start --only dataconnect
+
+# Generate SDKs
+firebase dataconnect:sdk:generate
+
+# Deploy to Firebase
+firebase deploy --only dataconnect
+```
+
+## Key Directives Quick Reference
+
+| Directive | Purpose | Example |
+|-----------|---------|---------|
+| `@table` | Define PostgreSQL table | `type Movie @table { ... }` |
+| `@col` | Customize column name/type | `@col(name: "movie_id", dataType: "serial")` |
+| `@default` | Set default value | `@default(expr: "uuidV4()")` |
+| `@ref` | Foreign key reference | `author: User!` (implicit) or `@ref(fields: "authorId")` |
+| `@unique` | Unique constraint | `email: String! @unique` |
+| `@index` | Database index | `title: String! @index` |
+| `@searchable` | Enable full-text search | `title: String! @searchable` |
+| `@auth` | Authorization level | `@auth(level: USER)` or `@auth(expr: "auth.uid != nil")` |
+| `@check` | Validate field in mutation | `@check(expr: "this != null", message: "Not found")` |
+| `@redact` | Hide field from response | Used with @check for auth lookups |
+| `@transaction` | Atomic multi-step mutation | `mutation Multi @transaction { ... }` |