feat(cli): modernize config setup and add completions

[calmcacil]

Summary

• replace the partial linear config setup with a validated section menu and complete guided flow
• expose every persisted configuration field, including add/edit/remove workflows for Sonarr and Radarr instances
• generate bash, zsh, and fish completion scripts with known flag-value suggestions
• preserve environment-only credentials during config edits and expand configuration validation
• document setup and completion installation across the Linux-supported shells

Testing

• make check
• go run github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.2 run --timeout=5m
• go run github.com/rhysd/actionlint/cmd/actionlint@v1.7.12
• go run golang.org/x/vuln/cmd/govulncheck@v1.6.0 ./...
• go test ./... (after rebasing onto origin/main)

Notes

• no new Go modules or dependencies
• configuration schema remains at version 1
• completion intentionally supports bash, zsh, and fish only because CalmsToolkit is Linux-focused