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

pysim_otaman_server/server.py

@@ -18,7 +18,7 @@ from osmocom.construct import GsmOrUcs2Adapter
 from osmocom.tlv import BER_TLV_IE
 
 
-VERSION = '1.9.2'
+VERSION = '1.9.3'
 
 
 # Static file serving (the PWA lives in <repo>/frontend, served by this server