e2e: cover IP ownership proof enforcement in user creation

[elitegreg]

Part of RFC-27 (tracker: #4194). Depends on #4197, #4201, and #4204.

What

Tests in e2e/:

• Flag off, no proof: user creation succeeds (the pre-RFC-27 path still works).
• Flag on, valid proof: user created, tunnel provisioned, BGP established — the full connect path, not just the instruction.
• Flag on, no proof: rejected with the expected error.
• Flag on, proof for a different IP: rejected.
• Flag on, stale-epoch proof: rejected.
• Wildcard/EdgeSeat pass with the flag on: creation requires a proof and binds the observed IP, which is the case RFC-27 exists for.
• Verifier key rotated via SetAuthority: proofs signed by the old key are rejected.

Acceptance

• Tests run under make e2e-test RUN=... individually, per the repo's guidance on not running the full suite concurrently.