fix(frontend): enforce dns-safe cluster names in byoc create form

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[abcxff]

Stack for rivet-dev/actors

• #5719 fix(frontend): poll byoc cluster regions on a 5s interval
• #5720 fix(frontend): decode region restarted time from operator bo …
• #5718 fix(frontend): enforce dns-safe cluster names in byoc create … 👈
• #5654 fix(workflow-engine): clear pruned loop history via batched, …
• main

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[the-company-company]

✅ No issues found

_{Reviewed commit a7fa909.}

[claude]

Review

Small, focused fix. Verified how it's wired end-to-end:

• byocDetailsSchema is only applied via schema: (values) => values.plan === "byoc" ? byocDetailsSchema : detailsSchema. I confirmed stepper-form.tsx (resolveSchema / Content's zodResolver wiring, and StepPanel's isStepValid check) already supports a function-typed Step.schema and re-resolves it against live form values on every render, so this correctly gates both the "Continue" button state and the actual RHF validation for the byoc path. Not dead code.
• Confirmed values.name is sent directly as the cluster name to client.byoc.createCluster(data.name, ...) (cloud-data-provider.tsx), so client-side DNS-safety validation here is legitimate, not speculative hardening.
• The regex (^[a-z0-9]([a-z0-9-]*[a-z0-9])?$, 1-63 chars) is a standard RFC 1123 DNS-label pattern, matching this repo's own convention ("name... must be valid DNS subdomain, kebab case") documented in the root CLAUDE.md.

Notes (non-blocking)

1. Backend parity unverified. The actual BYOC cluster-create handler lives in rivet-dev/engine-ee (this repo only has the generated @rivet-gg/cloud SDK client), so I couldn't confirm the API enforces the same regex/length. If the backend's constraint differs (e.g. a different max length or additional reserved-name checks), the frontend could either reject valid names or accept names the API then rejects with a raw API error. Worth a quick check against the engine-ee handler.
2. .min(1) is redundant — the regex already requires at least one character (the optional group only extends beyond the first char), so .min(1) never fires independently. Harmless, but could be dropped for conciseness.
3. No test coverage added, though this matches the existing file (no test/story file exists for create-project-form.tsx today), so this isn't a regression in practice.
4. Minor/pre-existing (not introduced by this PR): the shared Name field's placeholder still reads "Enter a project name..." even on the byoc "Create cluster" step. Not something this diff needs to fix, just noting it's adjacent.

Overall: correct, minimal, and consistent with the codebase's naming conventions. No security or performance concerns for a client-side regex validator.