User Profile: AI-Assisted Bio Summary (not needed)

## Goal

Add a one-line bio field to the user profile, generate it using AI from the user's existing bio, and surface it on the user profile and library intro card.

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## Scope

Full-stack: profile field, AI generation, DB storage, and display on two surfaces.

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## Background

Library intro cards on the homepage require a short, consistent bio for authors and maintainers. Rather than generating this ad hoc, the one-line bio is authored and stored on the user profile, then pulled from the database wherever needed.

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## Acceptance Criteria

### Profile field

- A "One Line Bio" text field is added to the edit profile page, below the biography field.
- Maximum character limit: 70 characters. A live character counter displays remaining characters.
- Placeholder text: "A short summary of your bio for library promotion."
- The field is plain text — no rich text or markdown.
- The field is saved to the database only when the user clicks "Save changes" in the Profile section. Auto-generated content is not saved automatically — the user must save manually.
### AI auto-generate

- An "Auto-Generate" button is displayed below the one-line bio field.
- On click, the user's existing biography is passed to the AI function, which returns a summary capped at 70 characters.
- The generated summary is populated into the one-line bio field. It is not saved to the database until the user clicks "Save changes".
- The user can edit the generated content after it has been populated.

**Button states:**

- **Idle:** "Auto-Generate" — button is enabled and visible.
- **Generating:** Button is disabled. A message is displayed: "Hold on! We are generating your one line bio summary, it may take a few seconds."
- **Generated:** The button is hidden. Auto-generation is a one-time action — once triggered, the button does not reappear.
### Display surfaces

- **User profile header:** The one-line bio is displayed on the user's public profile.
- **Library intro card:** The one-line bio is pulled from the database and displayed on the library intro card for authors and maintainers. If no one-line bio has been set, the bio field is empty on the library intro card.
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## FE/BE Actions

| Description | URL |
|---|---|
| Fetch user profile including one-line bio | |
| Save one-line bio | |
| Generate one-line bio from existing bio | |

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## Out of Scope

- Library intro card component (already exists)