Localize the GUI chrome

[BiosSystem]

Second half of localization for v3.5.0. Covers the 194 literal strings across the nine XAML schemas that #24 left untouched.

Substitution before parse, not a tree walk

My first instinct was to walk the loaded window and set properties. Measuring killed it: a logical tree does not contain text inside a Style or a template, and MainWindow carries 113 literal strings but exposes only 99 as logical tree nodes. A tree walk would have silently missed fourteen. Substituting on the markup before XamlReader parses it reaches all of them.

Keying

Source-string keys, i.e. the key is the English text.

• Positional keys (Content_01) break the moment anyone reorders markup. I built that first and threw it away.
• x:Name keys would work, but only 46% of the strings sit on a named element, so it meant adding identifiers to 103 elements across nine files.
• Source-string keys are stable under reordering, show the translator the original, and resolve to themselves when untranslated.

Values are read XML-decoded and written back XML-encoded, so a translation containing & or < cannot corrupt the markup. Attribute values opening with a brace are skipped as bindings.

All nine load sites now call Get-LocalizedXaml rather than reading the schema directly, keeping this to one integration point.

Two extraction problems

• 41 values are icon glyph character references (), not text. Excluded. This is why SharedStyles.xaml gets zero substitutions - all three of its strings are glyphs or a TemplateBinding.
• Three phrases differ only in capitalization (Restore backup/Restore Backup, Current User/Current user). ConvertFrom-Json cannot hold those as distinct PSCustomObject properties and threw. They now share one entry and resolve through case-insensitive property lookup, which I verified rather than assumed.

Verification

Loaded every schema through XamlReader headlessly with all 123 entries translated:

AboutWindow.xaml                  10 substituted  parse=OK
ApplyChangesWindow.xaml           10 substituted  parse=OK
AppSelectionWindow.xaml            9 substituted  parse=OK
BubbleHint.xaml                    1 substituted  parse=OK
ImportExportConfigWindow.xaml      3 substituted  parse=OK
MainWindow.xaml                   85 substituted  parse=OK
MessageBox.xaml                    5 substituted  parse=OK
RestoreBackupWindow.xaml          30 substituted  parse=OK
SharedStyles.xaml                  0 substituted  parse=OK

Also confirmed a translation containing &, < and a double quote is encoded correctly, and that MainWindow's 192 bindings are identical before and after.

A test asserts every translatable schema string has a catalogue entry, so adding a string without one fails the build. 23 localization tests total.

Static validation passes (112 files), standalone rebuilt and parse-checked.

Not verified: the GUI has not been displayed. Windows are constructed and parsed, which is the step substitution could break, but nothing has been rendered on screen.