feat(ga-agent): Add GA Agent project with decomposed architecture

Create workspace for building Google Analytics Claude Skill with:
- 5 independent components (MCP setup, skill, dimension explorer, Slack reporter, realtime watcher)
- Comprehensive project plan and documentation
- Step-by-step setup guides for each component

Components:
1. MCP Setup - GA4 + BigQuery MCP server installation
2. GA Agent Skill - Core Claude Skill for interactive analysis
3. Dimension Explorer - Validate dims/metrics with explanations
4. Slack Reporter - Automated reports to Slack (P2)
5. Realtime Watcher - Real-time monitoring (deferred)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ga-agent-project/docs/01-mcp-servers-overview.md

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+# MCP Servers Overview for GA Agent
+
+## Available MCP Servers
+
+### Google Analytics MCP Servers
+
+| Server | Language | Source | Status |
+|--------|----------|--------|--------|
+| **google-analytics-mcp** (Official) | Python | [googleanalytics/google-analytics-mcp](https://github.com/googleanalytics/google-analytics-mcp) | Recommended |
+| mcp-server-google-analytics | TypeScript | [ruchernchong/mcp-server-google-analytics](https://github.com/ruchernchong/mcp-server-google-analytics) | Community |
+
+**Official Google GA MCP Features:**
+- Real-time reporting
+- Custom/standard dimensions/metrics
+- Natural language queries (e.g., "top products by revenue")
+- `order_by` support
+- OAuth + Service Account auth
+
+### BigQuery MCP Servers
+
+| Server | Language | npm | Status |
+|--------|----------|-----|--------|
+| **@ergut/mcp-bigquery-server** | Node.js | `npx -y @ergut/mcp-bigquery-server` | Recommended |
+| mcp-server-bigquery | Python | - | Alternative |
+| Google MCP Toolbox | Python | - | Official (multi-DB) |
+
+**ergut/mcp-bigquery-server Features:**
+- Read-only secure access
+- Schema discovery
+- Natural language to SQL
+- 1GB query limit
+
+## Recommended Stack
+
+For our GA Agent, we recommend:
+
+```
+┌─────────────────────────────────────────────────────┐
+│                   Claude Code                        │
+│                        │                             │
+│           ┌───────────┴───────────┐                 │
+│           ▼                       ▼                 │
+│  ┌─────────────────┐    ┌─────────────────┐        │
+│  │ Google Analytics│    │    BigQuery     │        │
+│  │   MCP Server    │    │   MCP Server    │        │
+│  └────────┬────────┘    └────────┬────────┘        │
+│           │                      │                  │
+│           ▼                      ▼                  │
+│  ┌─────────────────┐    ┌─────────────────┐        │
+│  │  GA4 Data API   │    │  BigQuery API   │        │
+│  │  GA4 Admin API  │    │  (GA4 Export)   │        │
+│  └─────────────────┘    └─────────────────┘        │
+└─────────────────────────────────────────────────────┘
+```
+
+## Why Both?
+
+1. **GA4 MCP** - Direct API access for:
+   - Real-time data
+   - Quick metrics queries
+   - Account/property management
+
+2. **BigQuery MCP** - For advanced analysis:
+   - Historical data (GA4 → BigQuery export)
+   - Complex SQL queries
+   - Cross-dataset joins
+   - Large-scale analysis
+
+## Prerequisites
+
+### Google Cloud Setup
+
+1. Create a Google Cloud Project (or use existing)
+2. Enable these APIs:
+   - Google Analytics Data API
+   - Google Analytics Admin API
+   - BigQuery API
+
+3. Create Service Account:
+   - Go to IAM & Admin → Service Accounts
+   - Create new service account
+   - Grant roles:
+     - `Analytics Viewer` (or Admin for write ops)
+     - `BigQuery Data Viewer`
+     - `BigQuery Job User`
+   - Download JSON key file
+
+4. Grant GA4 Access:
+   - In GA4 Admin → Property Access Management
+   - Add service account email with Viewer role
+
+## Next Steps
+
+See `02-setup-guide.md` for installation instructions.