Refactor billing API and remove deprecated connection/view endpoints (#60)

## Summary
This PR implements a significant refactoring of the robosystems client
by updating billing API status handling and removing deprecated
connection and view management functionality. The changes streamline the
codebase by eliminating unused endpoints and consolidating
subscription-related models.

## Key Accomplishments
- **Updated Billing API**: Refactored checkout status endpoint with
improved status value handling
- **Removed Connection Management**: Eliminated entire connections API
module including:
  - Connection CRUD operations (create, get, delete, list)
  - OAuth flow endpoints (init, callback, token exchange)
  - Link token management
  - Connection synchronization
- **Removed View Management**: Deleted view creation and management
endpoints
- **Model Cleanup**: Removed 30+ obsolete model classes related to
connections and views
- **Subscription Model Updates**: Consolidated graph subscription models
and simplified tier management

## Breaking Changes
⚠️ **This is a breaking change** - The following functionality has been
completely removed:
- All connection management APIs (`/connections/*` endpoints)
- View creation and management APIs (`/views/*` endpoints)
- Related model classes for connections, OAuth flows, and view
configurations
- Provider-specific configurations (Plaid, QuickBooks, SEC)

Applications using these endpoints will need to be updated before
upgrading to this version.

## Files Impacted
- **Modified**: 6 files (billing API + subscription models)
- **Deleted**: 55 files (connections, views, and related models)
- **Total**: 61 files changed

## Testing Notes
- Verify billing checkout status API continues to function with updated
status handling
- Confirm subscription-related functionality works with consolidated
models
- Test that removal of connection/view endpoints doesn't impact other
API functionality
- Validate that import statements across the codebase have been properly
updated

## Infrastructure Considerations
- This change significantly reduces the client library footprint
- Applications should verify compatibility before deploying
- Consider versioning strategy for clients that still require
connection/view functionality
- Monitor for any residual dependencies on removed models in downstream
services

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

**Branch Info:**
- Source: `feature/improved-checkout`
- Target: `main`
- Type: feature

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

Author: jfrench9

robosystems_client/api/billing/get_checkout_status.py

@@ -69,10 +69,11 @@ def sync_detailed(
   **Status Values:**
   - `pending_payment`: Waiting for payment to complete
   - `provisioning`: Payment confirmed, resource being created
-  - `completed`: Resource is ready (resource_id will be set)
+  - `active`: Resource is ready (resource_id will be set)
   - `failed`: Something went wrong (error field will be set)
+  - `canceled`: Payment was canceled
 
-  **When status is 'completed':**
+  **When status is 'active':**
   - For graphs: `resource_id` will be the graph_id, and `operation_id` can be used to monitor SSE
   progress
   - For repositories: `resource_id` will be the repository name and access is immediately available
@@ -114,10 +115,11 @@ def sync(
   **Status Values:**
   - `pending_payment`: Waiting for payment to complete
   - `provisioning`: Payment confirmed, resource being created
-  - `completed`: Resource is ready (resource_id will be set)
+  - `active`: Resource is ready (resource_id will be set)
   - `failed`: Something went wrong (error field will be set)
+  - `canceled`: Payment was canceled
 
-  **When status is 'completed':**
+  **When status is 'active':**
   - For graphs: `resource_id` will be the graph_id, and `operation_id` can be used to monitor SSE
   progress
   - For repositories: `resource_id` will be the repository name and access is immediately available
@@ -154,10 +156,11 @@ async def asyncio_detailed(
   **Status Values:**
   - `pending_payment`: Waiting for payment to complete
   - `provisioning`: Payment confirmed, resource being created
-  - `completed`: Resource is ready (resource_id will be set)
+  - `active`: Resource is ready (resource_id will be set)
   - `failed`: Something went wrong (error field will be set)
+  - `canceled`: Payment was canceled
 
-  **When status is 'completed':**
+  **When status is 'active':**
   - For graphs: `resource_id` will be the graph_id, and `operation_id` can be used to monitor SSE
   progress
   - For repositories: `resource_id` will be the repository name and access is immediately available
@@ -197,10 +200,11 @@ async def asyncio(
   **Status Values:**
   - `pending_payment`: Waiting for payment to complete
   - `provisioning`: Payment confirmed, resource being created
-  - `completed`: Resource is ready (resource_id will be set)
+  - `active`: Resource is ready (resource_id will be set)
   - `failed`: Something went wrong (error field will be set)
+  - `canceled`: Payment was canceled
 
-  **When status is 'completed':**
+  **When status is 'active':**
   - For graphs: `resource_id` will be the graph_id, and `operation_id` can be used to monitor SSE
   progress
   - For repositories: `resource_id` will be the repository name and access is immediately available