Stake Lock as Owner Alpha on Subnet Registration

[JohnReedV]

Summary

This PR updates subnet registration so the owner key receives initial staked alpha at registration time.

Previously, subnet registration only:

• locked the registration TAO,
• seeded the new subnet pool with network_min_lock,
• recycled the remainder,
• and set the subnet owner metadata.

The owner did not receive any initial alpha stake from the registration spend.

With this change, the owner now receives staked alpha equivalent to the TAO spent on registration, converted using the current median subnet alpha price at the time of registration.

In one line:
Registering a subnet now grants the owner initial staked alpha priced off the median subnet alpha market price.

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Registration flow change

After the registration lock is taken and the subnet is initialized:

1. the new subnet pool is still seeded using network_min_lock
2. the current median subnet alpha price is computed from existing subnets
3. the TAO actually spent on registration is converted into alpha using that median price
4. that alpha is assigned as staked alpha to the subnet owner hotkey/coldkey pair

This preserves the existing subnet initialization flow while adding an owner stake position at creation time.

[ales-otf]

can also be just !owner_alpha_stake.is_zero().