New localPathGrants.ts: an in-memory registry of paths the user picked in a
native dialog. Every check resolves realpath + stat at grant and use time;
Windows case folding; missing files, directories-as-files, devices and
symlinked parents can never pass. SFTP upload/download and zmodem send/
receive now refuse renderer-supplied local paths that were never granted,
returning the resolved path so callers never re-traverse a symlink. keyPath
is validated as a regular file <= 1MB before reading (a device node would
have blocked the UI thread forever). Tests inject a stub policy via
setLocalPathPolicy; production always defaults to the real registry.
Also: webPreferences now explicitly pins contextIsolation/nodeIntegration/
webSecurity instead of relying on defaults.
New offline test tests/local-path-grants.mjs (37 assertions incl. symlink
escape); offline suite grows to 13. i18n: 6 main.sftp/main.key error keys
in 4 languages.
