fix(web): polish project cards and onboarding (#233)

[AmzBG]

Description

• Sync upstream commit afd51f7 (fix(web): polish project cards and onboarding).
• Display project cover images or logos on the login page, with a gradient fallback when an image cannot load.
• Preserve manually edited developer slugs while continuing to generate slugs from display names when appropriate.
• Prevent long repository names from overflowing project-selection cards.
• Limit theme selection to explicit light and dark modes and remove leftover onboarding debug logs.

Link to issue or ticket

Upstream change: chrisshaddad/bootcamp-starter@afd51f7

Steps to QA

1. Run npx turbo run lint.
2. Run npx turbo run check-types.
3. Run npx turbo run build.
4. Open the login page and confirm project cards show a cover image, logo, or gradient fallback.
5. Complete developer onboarding, manually edit the public slug, and confirm later display-name edits do not overwrite it.
6. Open the new-project repository picker and confirm long repository names truncate without overflowing.
7. Confirm the theme menu offers only light and dark modes and that the selected theme persists.

Screenshots

Found here: chrisshaddad/bootcamp-starter#233