Refactor Go codebase into focused files

[cerede2000]

What changed

• splits the former 2,200-line src/main.go into focused Go files without changing runtime behavior;
• isolates configuration/profile lifecycle, Docker discovery and events, route policy/scope enforcement, HTTP proxy handling, and shared types;
• leaves src/main.go as application wiring only.

Why

The codebase now has clear boundaries for future engine support such as Podman while keeping the security policy and container-scope logic shared rather than duplicated.

User impact

No endpoint, profile key, permission, image, or authorization behavior changes. Existing deployments remain compatible.

Validation

• gofmt -w src/*.go
• git diff --check
• go test -race ./...
• go vet ./...