Refactor god classes: MigrationService (970 LOC), ThreeScaleService (758 LOC)

[pcastelo]

Problem

MigrationService.java is 970 LOC handling analyze, YAML generation, secret creation, AI prompt building, catalog parsing, and DevHub registration. Violates Single Responsibility Principle and is high regression risk.

Proposed extraction

• YamlResourceGenerator — YAML manipulation and resource assembly
• SecretGenerator — K8s secret creation for OIDC, API keys
• AiPromptBuilder — AI prompt construction for migration analysis
• CatalogInfoGenerator — DevHub catalog-info.yaml generation
• Keep MigrationService as thin orchestrator (~200 LOC)

Also refactor

• ThreeScaleService.java (758 LOC) — extract cache layer and CRD discovery
• MigrationResource.java (306 LOC) — extract input validation

Acceptance criteria

• No class exceeds 300 LOC
• Existing tests still pass after extraction
• New classes have dedicated unit tests
• No behavior change (pure refactoring)