Widgets: add shared WidgetTheme + BarGrid (foundation)

Groundwork for the slate-background / brand-orange widget re-theme and the
new bar-style event countdown:
- WidgetTheme (dark slate background, brand orange accent, text tones).
- BarGrid: vertical-bar (comb) progress view.

Re-theming the existing widgets and adding the bars widget follows.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

KisaniCal.xcodeproj/xcshareddata/xcschemes/KisaniCal.xcscheme

@@ -1,11 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "1500"
-   version = "1.7">
+   LastUpgradeVersion = "2620"
+   version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"
-      buildImplicitDependencies = "YES"
-      runPostActionsOnFailure = "NO">
+      buildImplicitDependencies = "YES">
       <BuildActionEntries>
          <BuildActionEntry
             buildForTesting = "YES"
@@ -27,8 +26,7 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
-      shouldUseLaunchSchemeArgsEnv = "YES"
-      onlyGenerateCoverageForSpecifiedTargets = "NO">
+      shouldUseLaunchSchemeArgsEnv = "YES">
       <MacroExpansion>
          <BuildableReference
             BuildableIdentifier = "primary"
@@ -40,8 +38,6 @@
       </MacroExpansion>
       <Testables>
       </Testables>
-      <CommandLineArguments>
-      </CommandLineArguments>
    </TestAction>
    <LaunchAction
       buildConfiguration = "Debug"
@@ -63,8 +59,6 @@
             ReferencedContainer = "container:KisaniCal.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
-      <CommandLineArguments>
-      </CommandLineArguments>
    </LaunchAction>
    <ProfileAction
       buildConfiguration = "Release"
@@ -82,8 +76,6 @@
             ReferencedContainer = "container:KisaniCal.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
-      <CommandLineArguments>
-      </CommandLineArguments>
    </ProfileAction>
    <AnalyzeAction
       buildConfiguration = "Debug">