Add Anna search flow to dashboard

[thuanhuynhh]

This PR adds a built-in Anna's Archive search flow to the Stacks dashboard.

Instead of only adding downloads by MD5 or direct URL, users can now search by title, author, or keyword, review matching results, and add the correct item to the queue directly from the web UI.

What changed

• Added a new backend search API at /api/search
• Scrapes Anna's Archive search results and returns structured result data
• Reuses working domain rotation and supports FlareSolverr fallback when needed
• Added a new dashboard search UI below the manual MD5/URL add box
• Added result cards with title, author, metadata, description, and per-item Add button
• Kept the original manual add flow unchanged

Why

This brings back the workflow from my older Go-based project:
search first, review a result list, then add the correct item into the queue.

Tested

• Logged into the dashboard successfully
• Verified /api/search returns live results
• Verified search results render in the UI
• Verified items can still be added manually by MD5/URL
• Verified the updated container runs healthy in Docker

[reversesh3ll]

I was just about to start working on this before I noticed your PR. So thanks! Hope it gets merged!