feat: add Apple container runtime support

[OVELYB]

Description

Add support for Apple's container CLI tool as a container runtime backend. The container tool (github.com/apple/container) runs Linux containers as lightweight VMs on macOS using the Virtualization framework, and is becoming increasingly popular as a Docker Desktop alternative on Apple Silicon Macs.

This PR:

• Adds runtime_container_apple.go implementing the ContainerRuntime interface for Apple container
• Parses container ls --format json --all output to list containers with full metadata (image, state, networks, mounts, ports, command)
• Implements Enrich() via container inspect to get accurate container start times
• Adds Apple container detection in container_detect.go for process-level container identification
• HostPID() returns 0 since VM-based containers have no direct host PID mapping

Note: container is macOS-only (uses the macOS Virtualization framework). The implementation is safe on Linux — Available() returns false when the binary is absent.

Type of change

Check all that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (may affect existing functionality)
• This change requires a documentation update

Checklist

• I have formatted my code using go fmt ./...
• I have opened this PR against the staging branch
• I have performed a self-review of my own code
• I have added helpful comments where needed
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

Test Plan

Environment: macOS 26 (Apple Silicon) with container installed via Homebrew.

Steps:

1. container system start — start the container daemon
2. container run -d --name test-nginx nginx:latest — start a test container
3. go run ./cmd/witr -i — launch witr TUI
4. Switch to the Containers tab — verify the container appears with correct ID, image, state, ports, and command
5. Select the container row — verify the detail pane shows full container metadata

Additional verification:

• go build ./... — compiles without errors on macOS
• go vet ./... — no warnings
• go test ./... — all existing tests pass (no regressions)
• Verified on Linux: runtime_container_apple.go compiles cleanly, Available() returns false since container binary doesn't exist on Linux

Screenshots