refactor(config): unify validator-count rules across modes

[kangeunchan]

Enhancement Description

Unify validator count rules across YAML/TOML/CLI paths to prevent late runtime failures and inconsistent behavior.

Summary

This PR introduces a single source of truth for validator count validation and applies it consistently across config and CLI entry points.

Previously, validator checks differed by path:

• deploy used mode-aware bounds (docker: 1-100, local: 1-4)
• some config/YAML paths effectively enforced 1-4 regardless of mode
• dvb provision had no upper bound check in flag mode

Now all relevant paths use one shared validator rule.

What Changed

1) SSOT validator function

Added shared mode-aware validation in:

• internal/config/validator.go
• internal/config/validator_test.go

Rules:

• local: 1-4
• docker: 1-100
• empty mode defaults to docker

2) Replaced inconsistent call sites with SSOT

Updated:

• internal/config/validate.go
  • EffectiveConfig.Validate() now validates validator count by mode
  • ValidateFileConfig() now validates validator count by mode (when mode is set; defaults to docker otherwise)
• internal/config/yaml_validator.go
• internal/config/yaml_config.go
• cmd/devnet-builder/commands/manage/deploy.go
• cmd/dvb/provision.go

3) Interactive path consistency

Updated interactive validator prompt to use the same mode-aware bounds:

• internal/config/interactive.go

4) Tests

Added/updated tests:

• internal/config/validate_test.go
• internal/config/validator_test.go
• internal/config/yaml_validator_test.go
• internal/config/yaml_config_test.go
• cmd/dvb/provision_test.go

Why This Is Needed

This is a consistency bugfix, not a semantic change:

• the documented/runtime intent already included mode-specific bounds
• validation behavior differed by entry point
• invalid config could pass one path and fail later after expensive provisioning steps

Behavior Notes / Regression Impact

This may tighten validation for users who previously relied on permissive or inconsistent paths.
Example: values that passed some YAML/TOML flows but violate mode-specific constraints now fail early with consistent errors.

Validation Performed

• go test ./internal/config/...
• go test ./cmd/devnet-builder/commands/manage/...
• go test ./cmd/dvb/...
• go test ./...

golangci-lint run was also executed; repository has existing baseline lint issues outside this PR scope.