Feat: plugin based architecture and DevTokens solution

[rian-be]

This PR establishes AuthKit as plugin based service and delivers the first solution on top of it.

• introduces the IAuthKitPlugin contract and dynamic plugin loading from plugins/ directory
• adds the DevTokens plugin for issuing, validating, listing, and revoking developer tokens
• restructures the codebase under src/ (Core / Host / Plugins) and migrates the solution, CI, and Docker layout
• moves Keycloak realm configuration into the Deploy/ folder

Plugin Architecture

• adds AuthKit.Plugins.Abstractions with IAuthKitPlugin, AuthKitSecuritySchemeDescriptor, AuthKitSecuritySchemeType, and AuthKitApiKeyLocation
• IAuthKitPlugin lets plugin contribute services, middleware, health checks, and OpenAPI security schemes without being referenced by the host
• adds PluginLoader and LoadedPlugin that discover and load plugin assemblies from AuthKit:PluginsPath at startup
• the host calls ConfigureServices, inserts contributed middleware, exposes security schemes, and reports plugin health

DevTokens Plugin

• adds DevTokensPlugin registered as an IAuthKitPlugin (issues and validates developer tokens for SDK access)
• adds services IDeveloperTokenService, IDeveloperTokenManager, IDeveloperTokenValidator, and IDeveloperTokenRepository
• adds CQRS handlers (Wolverine) for create, delete, get-by-id, and list developer tokens with FluentValidation validators
• adds REST controllers: DeveloperTokensController, TokenLifecycleController, and VirtualMachineController
• adds DeveloperTokenMiddleware and scope based authorization (DeveloperScopeRequirement, DeveloperScopePolicyProvider, DeveloperScopeHandler)
• exposes the X-Developer-Token API key security scheme in OpenAPI
• adds value objects TokenName, TokenLifetime, and TokenScope, plus DeveloperTokenLimitExceededException

Core & Key Management

• moves the Core project under src/Core (domain, key management, token key bindings, options)
• key management provides RSA signing key generation, AES encrypted on disk key storage, JWT key store, and JWKS discovery
• token key bindings associate issued tokens with their signing key

Solution Layout & CI

• migrates from the legacy RyzeSDK.AuthKit.sln to AuthKit.slnx and adds Directory.Packages.props
• updates Dockerfile and docker-compose.yml to the new layout (host build/publish, plugin publish into plugins/, PostgreSQL + Keycloak services)
• updates .github/workflows/main.yml to build/test the new solution layout

Keycloak Configuration

• moves Keycloak realm definitions (realm-authz.json, workspace-authz-authz-config.json) into Deploy/Keycloak/realms

Result

• AuthKit is now an extensible host where new SDK solutions ship as plugins instead of changing the host
• developer token lifecycle (create, verify, list, get, delete, revoke-rotate) is served over REST
• the repository builds, containers, and runs from a single src/ based layout