The Fail callback was routing errors through the slog logger, which meant:
- Errors appeared as structured log messages (with timestamp and level)
- --log-level never silently swallowed errors
- --log-format json wrapped errors in JSON

Errors are now always printed directly to stderr as "Error: <message>",
independent of log configuration.

Default log level changed from "info" to "never"; server start-dev
continues to default to "warn" via its existing ChangedFromDefault
override. Users can still opt in with --log-level on any command.

Two deprecation warnings (namespace arg, env command args) converted
from logger calls to direct stderr writes so they remain visible
regardless of log level.

Convert CLI diagnostic messages (env/config file operations, env-var
flag overrides) from structured slog output to plain-text stderr gated
on --verbose. The structured logger now exists solely for the SDK client
and dev server, which conventionally use it.

--verbose should reveal non-obvious behavior (e.g. env var overriding
a flag), not echo what the user just asked to happen.

Set cctx.Verbose before populateFlagsFromEnv so it can call
printVerbose immediately, eliminating the deferred callback.

The only printVerbose call site was unreachable (the sole flag with an
env var annotation is --env, which is consumed before
populateFlagsFromEnv runs). Replace with an unconditional warning to
stderr so it works if BindFlagEnvVar is used for other flags in future.