Create Azure adapter: SQLServerFailoverGroup (#4539)

<!-- CURSOR_AGENT_PR_BODY_BEGIN -->
## Summary

Creates a new Azure adapter for SQL Server Failover Groups, following
the azure-adapter-creation skill workflow.

## Changes

### New Files
- `sources/azure/clients/sql-failover-groups-client.go` - Client
interface for Azure SQL Failover Groups SDK
- `sources/azure/manual/sql-server-failover-group.go` -
SearchableWrapper adapter implementation
- `sources/azure/manual/sql-server-failover-group_test.go` - Unit tests
- `sources/azure/integration-tests/sql-server-failover-group_test.go` -
Integration tests (requires SQL admin credentials)
- `sources/azure/shared/mocks/mock_sql_failover_groups_client.go` -
Generated mock

### Modified Files
- `sources/azure/manual/adapters.go` - Registered the adapter

## Implementation Details

- **Wrapper type**: SearchableWrapper (client.Get takes
resourceGroupName, serverName, failoverGroupName)
- **UniqueAttribute**: Composite key via
`shared.CompositeLookupKey(serverName, failoverGroupName)`
- **SDK package**: `armsql/v2` (already in go.mod)
- **Parent adapter**: `sql-server.go` already has SEARCH link to this
child type

### Linked Items
- Parent SQL Server (GET)
- Partner servers (GET with cross-resource-group scope extraction)
- Databases in the failover group (GET with composite key)
- Read-only endpoint target server (GET)

### Health Mapping
- Empty string / normal → HEALTH_OK
- CATCH_UP, PENDING, SEEDING → HEALTH_PENDING
- SUSPENDED → HEALTH_WARNING
- Unknown states → HEALTH_UNKNOWN

## Self-Review Checklist

- [x] **IAMPermissions**: Present, references
`Microsoft.Sql/servers/failoverGroups/read`
- [x] **PredefinedRole**: Present, uses `Reader`
- [x] **LinkedItemQueries**: 4 link types verified (parent server,
partner servers, databases, target server)
- [x] **PotentialLinks**: 2 types listed (SQLServer, SQLDatabase),
matches LinkedItemQueries
- [x] **Unit tests**: All passing (Get, Search, SearchStream,
StaticTests, ErrorHandling, edge cases)
- [x] **Integration test**: Present and structurally correct (skips when
SQL admin credentials not available)

All checklist items passed. Ready for review.

## Testing

Unit tests pass:
```
=== RUN   TestSqlServerFailoverGroup
--- PASS: TestSqlServerFailoverGroup (0.03s)
    --- PASS: TestSqlServerFailoverGroup/Get
    --- PASS: TestSqlServerFailoverGroup/Get_WithInsufficientQueryParts
    --- PASS: TestSqlServerFailoverGroup/GetWithEmptyServerName
    --- PASS: TestSqlServerFailoverGroup/GetWithEmptyFailoverGroupName
    --- PASS: TestSqlServerFailoverGroup/Search
    --- PASS: TestSqlServerFailoverGroup/SearchStream
    --- PASS: TestSqlServerFailoverGroup/SearchWithEmptyServerName
    --- PASS: TestSqlServerFailoverGroup/Search_InvalidQueryParts
    --- PASS: TestSqlServerFailoverGroup/Search_WithNilName
    --- PASS: TestSqlServerFailoverGroup/ErrorHandling_Get
    --- PASS: TestSqlServerFailoverGroup/ErrorHandling_Search
    --- PASS: TestSqlServerFailoverGroup/InterfaceCompliance
```

Linting passes:
```
golangci-lint run ./sources/azure/...
0 issues.
```

Resolves ENG-3551
<!-- CURSOR_AGENT_PR_BODY_END -->

Linear Issue:
[ENG-3551](https://linear.app/overmind/issue/ENG-3551/create-azure-adapter-sqlserverfailovergroup)

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Lionel Wilson <Lionel-Wilson@users.noreply.github.com>
GitOrigin-RevId: b1a861686385e61721059943f5ab67671b29a93b

Author: 2 people

sources/azure/clients/sql-failover-groups-client.go

@@ -0,0 +1,35 @@
+package clients
+
+import (
+	"context"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/resourcemanager/sql/armsql/v2"
+)
+
+//go:generate mockgen -destination=../shared/mocks/mock_sql_failover_groups_client.go -package=mocks -source=sql-failover-groups-client.go
+
+// SqlFailoverGroupsPager is a type alias for the generic Pager interface with failover groups response type.
+type SqlFailoverGroupsPager = Pager[armsql.FailoverGroupsClientListByServerResponse]
+
+// SqlFailoverGroupsClient is an interface for interacting with Azure SQL Server Failover Groups
+type SqlFailoverGroupsClient interface {
+	ListByServer(ctx context.Context, resourceGroupName string, serverName string) SqlFailoverGroupsPager
+	Get(ctx context.Context, resourceGroupName string, serverName string, failoverGroupName string) (armsql.FailoverGroupsClientGetResponse, error)
+}
+
+type sqlFailoverGroupsClient struct {
+	client *armsql.FailoverGroupsClient
+}
+
+func (a *sqlFailoverGroupsClient) ListByServer(ctx context.Context, resourceGroupName string, serverName string) SqlFailoverGroupsPager {
+	return a.client.NewListByServerPager(resourceGroupName, serverName, nil)
+}
+
+func (a *sqlFailoverGroupsClient) Get(ctx context.Context, resourceGroupName string, serverName string, failoverGroupName string) (armsql.FailoverGroupsClientGetResponse, error) {
+	return a.client.Get(ctx, resourceGroupName, serverName, failoverGroupName, nil)
+}
+
+// NewSqlFailoverGroupsClient creates a new SqlFailoverGroupsClient from the Azure SDK client
+func NewSqlFailoverGroupsClient(client *armsql.FailoverGroupsClient) SqlFailoverGroupsClient {
+	return &sqlFailoverGroupsClient{client: client}
+}