fix: use font= for system fonts and avoid duplicate fontfile= in buildTextFilter

[sudha09-git]

Fixes #1243

Problem

buildTextFilter in src/lib/text-overlay.ts had two bugs:

1. System fonts (Arial, Roboto, Poppins etc.) were passed as
   fontfile='Arial' — but fontfile expects a filesystem path, not a
   font name. FFmpeg silently fell back to its default font (Vera),
   so the user's chosen font was never applied to the exported video.

2. Custom uploaded fonts ended up with duplicate fontfile= arguments:
   fontfile='CustomName':fontfile=/path/to/font.ttf
   causing FFmpeg to reject the export entirely.

Fix

• System fonts now use :font='FamilyName' (correct FFmpeg parameter)
  only when no custom fontfile path exists
• Custom fonts continue using :fontfile=/path only, with no redundant
  font-family argument added

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[sudha09-git]

Hi @magic-peach

Just a gentle reminder on this PR — all CI checks are passing and this fixes two distinct FFmpeg font bugs (wrong parameter for system fonts + duplicate fontfile= for custom fonts) with a minimal 2-line change.

Could you please review when you get a chance? Happy to make any changes if needed!

[sudha09-git]

Hi! I've successfully fixed Issue #1243 in PR #1309.

Fix Summary:

• Changed system fonts to use :font='FamilyName' (correct FFmpeg parameter)
• Added !fontFileParam check to avoid duplicate fontfile= for custom fonts

Files Changed:

• src/lib/text-overlay.ts (2 lines added, 2 lines removed)

Testing:

• All 47 existing tests pass
• 3 test suites fail, but this is a pre-existing path alias issue
  (fails on main branch too - unrelated to my fix)

The PR is ready for review. Let me know if any changes are needed!