Fixed image upload crash and added URL paste support for profile images

[kushbosamiya]

fixing #215

Uploading an image on the shop profile or user profile page crashes with
"Cannot read properties of undefined (reading toString)"

This happens because the blossom server response is used directly without
checking the HTTP status or validating that the expected fields exist.
If the server returns an error or an incomplete response, response.size.toString()
blows up.

Additionally, users who already have images hosted on blossom or any URL
are forced to re-upload them -- there is no way to just paste a URL.

Changes

Bug fix -- blossom upload crash (nostr-helper-functions.ts)

• Check res.ok before parsing the JSON response
• Throw a descriptive error if the server returns a non-200 status
• Validate that response.url and response.sha256 exist before using them
• Use String(response.size) with a null check instead of bare .toString()

Feature -- paste image URL (file-uploader.tsx)

• Added an optional allowUrlInput prop to FileUploaderButton
• When enabled, renders a text input where users can paste an image URL directly
• Validates the URL before accepting it (must be http/https)
• Backward compatible -- existing callers without the prop are unaffected

Wired up URL paste on profile and community forms

• shop-profile-form.tsx (component)
• user-profile-form.tsx (component)
• pages/settings/shop-profile.tsx
• pages/settings/user-profile.tsx
• CreateCommunityForm.tsx

Testing

• Log in with Amber or any signer
• Go to shop profile settings, try uploading an image -- should no longer crash
• Paste a blossom/image URL into the new input field and click Use URL -- image should appear
• Same flow works on user profile and community creation forms

[vercel]

Someone is attempting to deploy a commit to the shopstr-eng Team on Vercel.

A member of the Team first needs to authorize it.