feat: integrate azure storage handling in migration pipeline

Stream transformer output to an Azure blob container when a job declares ToStorage, with per-job prefix and credential configuration.

.atl/skill-registry.md

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+# Skill Registry — go-migrate
+
+Generated: 2026-04-21
+
+## Compact Rules
+
+### Go conventions
+- Use existing error wrapping pattern: `fmt.Errorf("context: %w", err)`
+- Channel-based pipeline — keep goroutine lifecycle clean (close channels in correct order)
+- No comments unless non-obvious WHY; no docstrings
+- Prefer named returns only when it aids clarity in short functions
+- Use `strings.EqualFold` for case-insensitive column name comparison
+
+### Project conventions
+- Config structs live in `internal/app/config/`
+- ETL interfaces live in `internal/app/etl/types.go`
+- Transformer implementations in `internal/app/etl/transformers/`
+- Azure operations via `internal/app/azure/main.go`
+- Per-job transformer creation (not shared) when job has storage config
+
+## User Skills
+| Trigger | Skill |
+|---------|-------|
+| sdd-* | SDD workflow skills |