[Frontend] Add a dedicated create flow

[Kaylahray]

Description

Post creation is split across modals, but there is no dedicated create experience for composing a giveaway or help request with better validation, previews, and step-by-step guidance.

User Story

As a user,
I want to create a giveaway or help request through a guided flow,
so that I can complete the post confidently without missing required fields.

Requirements and Context

• Files: app/components/create-post-modal.tsx, app/components/create-giveaway-modal.tsx, app/components/create-request-modal.tsx, app/feed/page.tsx
• Add a structured create flow with type selection, preview, and final confirmation
• Reuse the existing API route for post creation
• Surface validation errors before submission

Suggested Implementation

// CREATE FLOW
// 1. Choose post type.
// 2. Collect type-specific fields.
// 3. Preview the post.
// 4. Submit to /api/posts.

Acceptance Criteria

• Users can create both giveaway and help request posts from a guided flow.
• Validation errors are visible before submission.
• Successful creation refreshes the feed without a full reload.

Submission Guidelines

• Branch: feat/create-flow
• Depends on: POST /api/posts
• PR: feat(frontend): add guided post creation flow

[Emmo00]

@Emmo00 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would love to work on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Emmo00 to this issue.

[SaintSammi]

@SaintSammi has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I want to work on this pls

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

[drips-wave]

Congratulations, @SaintSammi! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @SaintSammi: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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