Fix create-stream form start time picker accepting past timestamps without a warning

[Chuks-coderr]

Overview

The start time picker allows selecting dates and times in the past. The contract rejects past start times, but the user only finds out after signing the transaction — a poor experience.

Problem

Users who accidentally select a past start time waste a wallet signature and see a confusing contract error instead of an immediate form-level validation message.

Proposed Solution

• Add client-side validation on the start time field: if the selected time is in the past, show an inline error immediately
• Disable the submit button while the start time is invalid
• Re-validate on form focus (in case the user leaves the tab open and the selected time becomes past)

Acceptance Criteria

• Inline error shown immediately when start time is in the past
• Submit button disabled while start time is invalid
• Validation re-runs when the form regains focus
• No regression for valid future start times

[daniel007-ai]

@daniel007-ai has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

i can work on this issue sir

ℹ️ Repo Maintainers: To accept this application, review their application or assign @daniel007-ai to this issue.

[drips-wave]

Congratulations, @daniel007-ai! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

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