feat(config): add suppress_hook_warning option

Add hooks.suppress_hook_warning config option and RTK_SUPPRESS_HOOK_WARNING
env var to disable "No hook installed" and "Hook outdated" warnings.

Users running rtk via CLAUDE.md instructions instead of hooks, or with
tools like OpenCode, get these warnings on every command. The warnings
waste tokens and confuse AI agents since rtk is working correctly.

RTK_SUPPRESS_HOOK_WARNING=1 suppresses; any other value forces the warning
on; unset falls back to the config file. Both default to false so existing
behavior is unchanged. The env parse follows the repo's
as_deref() == Ok("1") convention.

The suppression check runs before status() so the suppressed path does not
pay for the hook probe.

Documented in configuration.md (the hooks block and the env var table) and
README.md.

Fixes #682

Signed-off-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>