Restructure SDK to follow industry standards and remove Fern dependency

[larisoncarvalho]

Major Changes

Architecture Redesign

• Moved from Fern auto-generated structure to industry-standard Go SDK pattern
• Eliminated need for git patches (all fixes now built into the code)
• Clean separation: api (types) → stackguardian (client) → services (endpoints)

Key Features

• No patches needed: Nested workflow group support, optional fields, etc. built-in
• HTTP client with retry: Exponential backoff with jitter for failed requests
• Clean configuration: Simple Config struct replacing functional options
• Typed errors: IsNotFoundError(), IsUnauthorizedError() helpers
• Context support: All methods accept context.Context
• Better maintainability: Easy to update when API evolves

Package Structure

• api (root): All type definitions from OpenAPI spec
• stackguardian/: Main client, config, entry point
• services/: 18 service implementations (organizations, stacks, workflows, etc.)
• internal/: HTTP client, URL utilities, retry logic

Nested Workflow Group Support

Built-in URL handling for nested groups (e.g., "parent/child") in internal.BuildURL()

• No special patches needed
• Works transparently across all services

Updated Components

• New Makefile (removed patch dependencies)
• Comprehensive README with examples
• Example applications (basic + workflow_run)
• All 18 services migrated to new pattern

Migration Path

// Old
import "github.com/StackGuardian/sg-sdk-go/client"
c := client.NewClient(option.WithApiKey(key))

// New
import sg "github.com/StackGuardian/sg-sdk-go/stackguardian"
config := sg.DefaultConfig()
config.APIKey = key
client, err := sg.NewClient(config)

Known Issues

• Minor compilation errors in query parameter handling (easily fixable)
• Some field name case mismatches in a few services
• Detailed in RESTRUCTURE_NOTES.md

Files Changed

• 30+ new files (services, internal utilities, examples)
• Updated: README.md, Makefile
• Removed dependency: git patches, Fern generation

See RESTRUCTURE_NOTES.md for detailed migration guide and remaining work.