fix(print): complete Windows printer discovery, honor the true default, surface failures; make CTB loading usable (#1261)

Printer enumeration used EnumPrinters level 4 only, which is served
from the local registry cache and misses Win11 per-user network
printers; an empty result now retries with level 2 (spooler RPC) and
merges the resolved default. The dialog's 'System default printer'
used to delegate to the shell print verb — the default PDF handler's
own printer choice, not the system default; it now resolves
GetDefaultPrinterW and dispatches printto naming that printer
explicitly. Every dispatch probes OpenPrinterW first, so a printer
that vanished between listing and printing produces a clear error
instead of ShellExecute's silent nothing, and all SE_ERR_* codes carry
readable reasons.

Legacy CTB: picking an unparseable table used to swallow the failure
(.ok()) — the user saw nothing at all. Load errors now reach the
command line, the picker accepts .stb alongside .ctb (the container
gains the STBVER1 header; .stb application errors state the actual
reason), and a table loaded from anywhere is copied into the user's
plot-styles folder so it persists in the dialog, matching AutoCAD.
Buffer parsing for both EnumPrinters layouts is unit-tested; the
missing-printer path was exercised against the real spooler (existence
probe only, no job).

Cargo.toml

@@ -62,7 +62,9 @@ fluent-syntax = "0.12"
 naga = { version = "27", features = ["wgsl-in"] }
 
 [target.'cfg(target_os = "windows")'.dependencies]
-windows-sys = { version = "0.61", features = ["Win32_UI_Shell", "Win32_UI_WindowsAndMessaging", "Win32_System_Com", "Win32_System_Registry", "Win32_Storage_FileSystem", "Win32_Foundation", "Win32_Graphics_Printing"] }
+# Win32_Graphics_Gdi + Win32_Security are required for PRINTER_INFO_2W (the
+# level-2 printer enumeration fallback in src/io/print_to_printer.rs).
+windows-sys = { version = "0.61", features = ["Win32_UI_Shell", "Win32_UI_WindowsAndMessaging", "Win32_System_Com", "Win32_System_Registry", "Win32_Storage_FileSystem", "Win32_Foundation", "Win32_Graphics_Printing", "Win32_Graphics_Gdi", "Win32_Security"] }
 
 [target.'cfg(target_os = "linux")'.dependencies]
 ashpd = { version = "0.13.13", default-features = false, features = ["async-io", "wayland"] }