Fix AI-generated pin description validation

[Dereje1]

Motivation

• AI-generated titles were being set into description but isDescriptionError remained stale (initially true), blocking save even when the generated title met the existing >=5 character rule.

Description

• Update handleAIimage() to trim the returned title, set it as description, and immediately recompute isDescriptionError using the existing description.trim().length < 5 rule in client/src/components/mypins/pincreatemodal.tsx.
• Add focused tests to tests/client/src/components/mypins/pincreatemodal.test.tsx to verify a valid generated title clears the description error and a short generated title remains invalid.
• Files changed: client/src/components/mypins/pincreatemodal.tsx, tests/client/src/components/mypins/pincreatemodal.test.tsx.

Testing

• Ran the focused Jest suite: npx jest tests/client/src/components/mypins/pincreatemodal.test.tsx --runInBand and all tests passed (21 tests, snapshots included).
• TypeScript checks: npm run compileTS completed successfully.
• Lint: npm run lint completed successfully.

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Codex Task