fix: honor create dry-run with explicit types

[dims]

A user running brev create --dry-run --type ... expects a safe preview of what the CLI would try, but today that path can still provision a real instance. In practice that means surprise spend, confusing behavior, and loss of trust in a flag that is supposed to be non-destructive. This PR fixes that command flow so dry-run consistently stays dry, even when instance types are supplied explicitly, and adds a regression test to keep it that way.

Summary

• short-circuit brev create --dry-run before any provisioning path, even when instance types come from --type or stdin
• print the explicit instance specs during dry-run instead of falling through into RunGPUCreate
• add a regression test covering --type ... --dry-run

Root cause

dry-run only returned early when no explicit instance types were provided. If --type was set, the command skipped the old dry-run branch and went on to create a real instance.

Validation

• go test ./pkg/cmd/gpucreate/...
• go test ./pkg/cmd/gpusearch/...
• built the patched CLI locally and verified:
  • /tmp/brev-local --no-check-latest create codex-dry-run-live-check --type hyperstack_H100 --dry-run --detached
  • /tmp/brev-local --no-check-latest create codex-dry-run-live-filter --gpu-name H100 --min-vram 80 --dry-run
• confirmed brev ls remained empty after both live checks

[Copilot]

Pull request overview

This PR fixes brev create --dry-run so it reliably short-circuits before any provisioning logic, including when instance types are explicitly provided via --type (or stdin), and adds a regression test to prevent the issue from returning.

Changes:

• Move the dry-run early return to occur immediately after parsing instance types (before any provisioning path can run).
• Enhance dry-run output to print explicit instance specs directly when they’re provided.
• Add a regression test ensuring --type ... --dry-run does not create workspaces.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/cmd/gpucreate/gpucreate.go	Ensures --dry-run always returns early; prints explicit instance specs when provided.
pkg/cmd/gpucreate/gpucreate_test.go	Adds a test that verifies dry-run with explicit types does not provision.

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[dims]

cc @theFong