Card presets + custom files: file & pasted JSON import, file export; v1.9.3

Both sections (card presets, custom files) gain two import paths and a
file download alongside the existing clipboard import:
- Import from file: hidden <input type=file accept=.json> + FileReader
  feeding the unchanged dedupe/merge logic (works on plain-HTTP LAN
  origins where navigator.clipboard is unavailable)
- Paste & import: reuses the IO textarea; guard requires '[' prefix so
  status messages are never mis-imported; empty state reveals + focuses
  the field with a hint placeholder
- Export to file: Blob download (otaman-cards.json /
  otaman-custom-files.json) via shared downloadJson() helper
- Import functions take optional text arg; clipboard stays the fallback
- data-l10n on all five buttons per section; LANG_RU entries for the
  three new labels

Version 1.9.2 -> 1.9.3 everywhere; SW cache otaman-v13 -> otaman-v14

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pysim-otaman-server"
-version = "1.9.2"
+version = "1.9.3"
 description = "HTTP REST server wrapping pysim for the OTAMan PWA"
 requires-python = ">=3.8"
 # pysim is a git-only dependency installed explicitly by setup.bat/setup.sh.