feat: unified shell, diagnostics pack, native Office, sticky board

Make Surface remote debugging and classroom workflows viable: always-on
structured logs with one-click zip export, a single AppShell chrome,
OOXML PPTX/DOCX annotation without LibreOffice, and a first-class sticky
board. Also drop spike/legacy ink widgets and tighten pen feel
(predictor, PenInfoHistory, page-tile layer).

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/l10n/app_en.arb

@@ -121,6 +121,18 @@
       "total": { "type": "int" }
     }
   },
+  "libraryTab": "Library",
+  "boardTab": "Stickies",
+  "shellTagline": "Ink · Annotate · Know",
+  "notesSection": "Notes",
+  "documentsSection": "Documents",
+  "emptyLibraryTitle": "Nothing here yet",
+  "emptyLibraryBody": "Create a note, or import PDF / PPT / Word",
+  "diagnosticsSection": "Diagnostics",
+  "diagnosticsExport": "Export diagnostic pack",
+  "diagnosticsExportHint": "Reproduce on Surface, export, and send the zip back",
+  "diagnosticsToggle": "Input diagnostics overlay",
+  "penSettingsUnified": "Pen & ink",
   "board": "Board",
   "boardTitle": "Sticky Board",
   "boardOpen": "Sticky note board",