Add multi-language syntax highlighting (#16)

Splash (Swift-only, since removed) left code rendering unhighlighted
everywhere. Add Highlightr (highlight.js) behind a small SyntaxHighlighter
service and use it on both surfaces:

- Native file viewer: highlight NSAttributedString by language inferred
  from the filename, picking a light/dark theme from the trait style and
  re-highlighting on style changes. Falls back to plain text for unknown
  languages or very large files.
- Markdown/org code blocks in the WKWebView (READMEs, tickets, comments):
  the web view disables JavaScript, so highlight server-side into inline
  color-styled spans. The color scheme is now part of the render/cache
  key since colors are baked into the HTML.

Covered by unit tests for language mapping and highlighted output.

1 files changed, 10 insertions, 1 deletions

diff --git a/Hutch.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved b/Hutch.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved
index 417e4d7..a268436 100644
--- a/Hutch.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved
+++ b/Hutch.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved
@@ -1,7 +1,16 @@
 {
-  "originHash" : "65542d8a5fbbad8dd7d07c8901c1cc48b3aba12cef8da1f062bd28d9b3a6ba50",
+  "originHash" : "4554417ca2693020116bce7cbda415a5e51ada6b4cc4a8b39f7f43a9644bb5e5",
   "pins" : [
     {
+      "identity" : "highlightr",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/raspu/Highlightr",
+      "state" : {
+        "revision" : "05e7fcc63b33925cd0c1faaa205cdd5681e7bbef",
+        "version" : "2.3.0"
+      }
+    },
+    {
       "identity" : "swift-cmark",
       "kind" : "remoteSourceControl",
       "location" : "https://github.com/swiftlang/swift-cmark.git",