[Fix] Modal Regions shows as a password field in Compute settings

[roomote-roomote-v1]

Opened on behalf of Matt Rubens. Follow up by mentioning @openmote, in the web UI, or in Slack.

What changed

Modal Regions in Settings → Compute (and setup advanced Modal settings) is a plain-text field, not a password input. Saved non-secret values are shown as readable text instead of bullet masks.

Clearing a saved optional non-secret setting (for example emptying Modal Regions after it was saved) now counts as a pending change so Save stays enabled, and save removes the stale deployment env var. The form no longer re-applies saved prefill from unstable query identities while you are editing. Real secrets still treat empty input as "leave unchanged."

Why this change was made

Modal Regions is placement configuration, not a credential. Password-style masking made it hard to read and edit. Follow-up review also found that clearing a saved regions value left Save disabled (and left the value unchanged), and the clearing test could be skipped when runtime MODAL_REGIONS leaked into CI/dev env.

Impact

Operators can see, edit, and fully clear optional plain-text compute settings like Modal Regions without the UI undoing the clear. Password treatment remains for true secrets only.

Screenshots

[roomote-roomote-v1]

No new code issues found. See task

• apps/web/src/components/settings/ComputeProviderSection.tsx:207 Clearing a saved non-secret optional compute value, such as MODAL_REGIONS, is treated as no pending change, so the Save button stays disabled. Even if another edit enables Save, saveComputeConfigCommand skips blank submissions and leaves the stale saved value in place. Support clearing persisted optional non-secret fields instead of only overwriting them with another non-empty value.
• apps/web/src/trpc/commands/compute/index.test.ts:297 The new clearing test is not isolated from a runtime MODAL_REGIONS value. With MODAL_REGIONS=us, buildSetupComputeStatus marks the field runtime-satisfied, saveComputeConfigCommand skips the delete path, and the test fails at txDelete not being called. Add MODAL_REGIONS to MANAGED_COMPUTE_ENV_VARS or explicitly stub/delete it in this test so it consistently exercises the saved-only clear path.