feat(manufacturers): add manufacturer logo support

[akira69]

--> opened too soon, coming later :)

Summary

Adds manufacturer logo support to FilaMan as a standalone PR based on main, without depending on the export or printing branches.

This PR introduces:

• backend manufacturer logo storage and URL import support
• manufacturer logo upload, serving, and clear endpoints
• manufacturer logo visibility in the manufacturer table and modal
• manufacturer logo visibility on filament and spool show/edit screens
• a backend startup fix so Alembic path resolution no longer depends on the process working directory

Plan reference:

• .copilot/logo-plan-pr857.md

Why

FilaMan needed the non-print manufacturer logo behavior inspired by Spoolman PR 857, but the work should be independent from the unrelated filament export/printing changes.

This branch is intentionally based on main and contains only the logo-related work.

Implementation

Backend

• Added logo_url and logo_file_path fields to manufacturers plus a migration.
• Added resolved_logo_url response support.
• Added manufacturer logo storage helpers.
• Added endpoints to:
  • upload a local logo file
  • import a logo from a remote URL into local storage
  • serve stored logo files
  • clear a stored logo
• Updated startup migration path handling to resolve backend/alembic.ini reliably regardless of launch cwd.

Frontend

• Added a shared manufacturer logo render helper.
• Added multipart upload support in the frontend API wrapper.
• Updated the manufacturer modal to support:
  • logo import from URL
  • local file upload
  • stored file path display
  • live logo preview
  • single clear action
• Added manufacturer logos to:
  • manufacturers list
  • filament detail
  • filament edit
  • spool detail
  • spool edit
• Refined the manufacturer modal UX:
  • internal scrolling
  • cleaner info modal layout
  • wide logo presentation
  • text fallback when no logo exists

Code Quality Compliance ✅

• Backend compile validation: passed with backend/.venv/bin/python -m compileall app
• Frontend build: passed with npm run build
• Fixed during validation:
  • logo import request schema so the backend accepts the intended { url } payload
  • Alembic startup pathing so backend launch no longer depends on cwd

Validation

Completed:

• Backend compile check on final branch
• Frontend build on final branch
• Live authenticated API smoke test for:
  • login
  • manufacturer create
  • logo import from URL into local storage
  • stored logo fetch from served endpoint
  • clear logo behavior

Notes:

• The original vendor-hosted test URL returned 429 Too Many Requests during one smoke test run, so the success-path validation used a stable public image URL instead.

Test Checklist

• Create a manufacturer with a logo imported from URL and verify preview appears in the modal
• Upload a local logo file for a manufacturer and verify the stored file path updates
• Clear a manufacturer logo and verify both preview and stored path are removed
• Confirm manufacturer table rows show wide logos without boxed thumbnails
• Confirm manufacturers without logos show the styled text fallback
• Confirm filament detail shows the manufacturer logo correctly
• Confirm filament edit updates the manufacturer logo preview when the manufacturer changes
• Confirm spool detail shows the selected filament manufacturer logo correctly
• Confirm spool edit updates the manufacturer logo preview when the filament changes
• Confirm manufacturer modal scrolling stays inside the modal rather than scrolling the page behind it