Switch verify gate defeated: validation marks switch_config_applied without verifying (regression from 2.2)

[sadsfae]

Summary

Environment validation marks a host switch_config_applied=True without
actually verifying the switchports. The "switch configuration missing" release
gate is effectively dead: an environment can pass network validation and be
released to a tenant even when the switch was never configured or the
configuration failed.

Root cause

Two layers each drop the real result:

1. src/quads/plugins/dispatchers/switch.py:43 SwitchDispatcher.verify awaits
   the plugin but discards its return value and hardcodes success:

try:
    await self._default_plugin.verify(host, cloud, change)
    return True
except Exception as e:
    logger.error(f"Failed to verify switch: {e}")
    return False

2. src/quads/plugins/builtin/switches/juniper.py:195 JuniperSwitchPlugin.verify
   never returns a value (all paths fall through or bare return), so it always
   yields None.

Consumer src/quads/plugins/builtin/validators/environment.py:238:

result = await self.switch_dispatcher.verify(host.name, previous_cloud, host.cloud.name)
if result:
    self.quads.update_host(host.name, {"switch_config_applied": True})
else:
    switch_config_missing.append(host.name)

Because the dispatcher always returns True (barring an exception), the host is
marked switch_config_applied=True with no verification, and
switch_config_missing is never populated.

Regression from 2.2

In 2.2, Switch.verify returned None and post_network_test used it directly
(result = switch.verify(...)); None is falsy, so an unverified host went into
switch_config_missing and validation FAILED (conservative hold). The dispatcher
refactor turned this into an unconditional True.

Impact

• The switch_config_applied hold is defeated at the validation gate:
  environments release without confirmed switch/VLAN configuration.
• Companion to Switch ports not configured on host move (async configure never awaited) #733, which fixed the move-time half of the same hold.

Fix

• SwitchDispatcher.verify should return the plugin's actual result.
• JuniperSwitchPlugin.verify should return True only when the switch state is
  confirmed/applied successfully for all interfaces, False otherwise (including
  not-found and failed set operations).