refactor(di): consolidate DI containers into a single tested implementation

[kangeunchan]

Enhancement Description

Consolidate DI container implementations into a single tested path to reduce ambiguity and wiring drift.

Summary

This PR standardizes DI construction on one canonical implementation and adds focused tests for wiring behavior.

Previously, multiple container paths increased maintenance risk:

• overlapping responsibilities across container/factory code
• inconsistent wiring behavior was harder to detect
• test coverage for integration points was limited

Now DI creation and wiring follow one clear path with dedicated tests.

What Changed

1) Consolidated DI creation path

Updated:

• internal/di/container_v2.go
• internal/di/factory.go

2) Removed duplicate wiring ambiguity

• unified adapter/container creation flow
• reduced parallel code paths for container assembly

3) Kept external behavior stable

• no public CLI/API contracts were changed
• composition semantics are preserved while code paths are simplified

4) Tests

Added/updated tests:

• internal/di/container_test.go
• internal/di/factory_test.go

Why This Is Needed

This is a maintainability and correctness refactor.
One container path improves readability, lowers review risk, and increases confidence in wiring changes.

Behavior Notes / Regression Impact

No intentional runtime behavior change.
Refactor scope is limited to DI internals and tests.

Validation Performed

• go test ./internal/di/...
• go test ./...
• golangci-lint run