feat: Implement Machine and NixosConfiguration types with kstatus compliance

[kitsunoff]

⚠️ TDD MANDATORY

Tests MUST be written BEFORE implementation code. No exceptions.

Write unit tests for type validation, default values, and kubebuilder markers FIRST.

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Description

Implement Go types for Machine and NixosConfiguration CRDs with full kstatus compliance.

Tasks

Machine Type

• Write tests for MachineSpec validation (required fields, patterns)
• Write tests for MachineStatus fields and conditions
• Implement MachineSpec with fields: host, sshUser, sshKeySecretRef, sshPasswordSecretRef
• Implement MachineStatus with observedGeneration
• Add status fields: discoverable, hasConfiguration, appliedConfiguration, appliedCommit, hardwareFacts, nixFacterResult
• Add standard conditions: Ready, Reconciling, Stalled, Discoverable, HardwareScanned
• Add kubebuilder markers for validation
• Add printer columns
• Verify all tests pass

NixosConfiguration Type

• Write tests for NixosConfigurationSpec validation
• Write tests for NixosConfigurationStatus fields and conditions
• Write tests for OperationState transitions
• Implement NixosConfigurationSpec with all fields (including jobTemplate)
• Implement NixosConfigurationStatus with observedGeneration
• Add OperationState for tracking long-running jobs
• Add status fields: fullDiskInstallCompleted, appliedCommit, configurationHash, additionalFilesHash
• Add standard conditions: Ready, Reconciling, Stalled, Applied, GitSynced
• Add kubebuilder markers for validation
• Add printer columns
• Verify all tests pass

Shared Types

• Write tests for condition helpers
• Define condition type constants
• Define reason constants
• Implement SecretReference type (same-namespace only)
• Implement MachineReference type
• Implement AdditionalFile type
• Implement JobTemplate type for job customization

Architecture Notes

• Machine addressing: Single host field (IP or hostname) - user provides working address
• Secret references: Same-namespace only (no cross-namespace) - projected volumes only work within namespace

Reference

See docs/kubebuilder-migration-analysis.md sections 3, 6, 7 for detailed type definitions.