fix: backward-compat + bug fixes and man-page build fix for 0.16.0

Post-0.15.0 review of the 0.15.0..HEAD range surfaced regressions and
bugs. This restores backward compatibility for existing configs/CSS,
fixes confirmed defects, and repairs the scdoc man-page build break on
master. Pango-markup tooltips are intentional and were kept.

Backward-compat restorations:
- AModule: honor legacy numeric Gdk::CursorType cursor values (int overload)
- memory: correct GiB divisor (was ~2.3% low); round bare {} placeholders
- wireplumber: scale max-volume into the linear domain so the cap works again
- idle_inhibitor: gate right/middle-click deactivate & scroll on dynamic-timeouts;
  accept both dynamic-timeout(s); widen timeout to double (no fractional truncation)
- custom: keep #custom-<name>.<class> CSS selectors working (classes on box_)
- image: don't wordexp-split a single path; fall back to the literal path
- niri/window: restore hide-when-empty (new show-empty opt-in); escape tooltip
- wlr/taskbar: plain-text tooltip when markup is disabled

Bug fixes:
- tray: fix use-after-free in onAdd; guard the watcher retry timeout
- hyprland: clamp max-windows iterator (OOB); drop duplicate language tooltip block
- niri/window: supply {col}/{max_col} args in the empty branch (fmt::format_error)
- mpris: escape {dynamic}/{player} tooltip; fix dangling player; albumArtist source
- mango: fix use-after-free race (dispatch under callback_mutex_)
- mpd: contain throwing checkErrors in noexcept idle paths (no std::terminate/UAF)
- keyboard_state: always render every lock label, with guarded defaults
- bluetooth: bound GATT ReadValue timeout, opt-in + services-resolved gating,
  preserve authoritative Battery1 percentage
- wireplumber: fix WpDevice reference leak / NULL handling
- battery, clock, dwl, wayfire, graph, custom_graph, transform, river: assorted
  crash/logic fixes

Man page / build:
- niri-workspaces: fix scdoc "indented by an amount greater than 1"
  (workspace-taskbar sub-options were mis-indented; breaks man-page build)
- document new show-empty (niri/window); correct network {txBitrate}/{rxBitrate}

Not compiled locally (no gtkmm on this host); C++ build relies on CI.
Man pages validated with scdoc 1.11.4.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/util/transform_8bit_to_rgba.cpp

@@ -3,6 +3,8 @@
 #include <iomanip>
 #include <regex>
 #include <sstream>
+#include <stdexcept>
+#include <system_error>
 namespace fs = std::filesystem;
 
 struct TransformResult {
@@ -12,11 +14,12 @@ struct TransformResult {
 
 TransformResult transform_8bit_to_hex(const std::string& file_path) {
   std::ifstream f(file_path, std::ios::in | std::ios::binary);
-  const auto size = fs::file_size(file_path);
-  std::string result(size, '\0');
-  if (!f.is_open() || !f.good()) {
+  std::error_code ec;
+  const auto size = fs::file_size(file_path, ec);
+  if (ec || !f.is_open() || !f.good()) {
     throw std::runtime_error("Cannot open file: " + file_path);
   }
+  std::string result(size, '\0');
 
   if (size == 0) {
     return {.css = result, .was_transformed = false};