fix(lint): enforce accessible SVG viewBox and title rules (#123)

* fix(lint): enforce viewBox presence and title length cap

- Add a11y check: non-decorative <svg> must carry a viewBox attribute
  with exactly four numeric tokens and positive width/height dimensions.
- Add a11y check: <title> text must be 60 characters or fewer, closing
  the gap between the CONTRIBUTING.md spec and linter enforcement.
- Update VALID_SVG in test-lint-a11y.py to include viewBox so all
  existing passing cases remain valid after the new checks land.
- Add three adversarial cases: missing-viewbox, invalid-viewbox,
  title-too-long — all verified against the gate suite (47/47 OK).

* fix(lint): accept SVG comma separators and reject non-finite viewBox values

- Re-split viewBox on [\s,]+ so comma-separated values (e.g. 0,0,800,600)
  are accepted as valid SVG
- Guard each component with math.isfinite() so values like inf and nan are
  rejected rather than passing the > 0 size check
- Add adversarial test cases: viewbox-comma-separated (pass),
  viewbox-nonfinite-width, viewbox-nonfinite-height (both fail)
- Bump plugin manifests to 2.4.1

* fix(lint): reject viewBox numbers with Python-only underscore separators

* test(lint): cover remaining viewBox cases

---------

Co-authored-by: Rupam Pal <rupam.pal@euromonitor.com>

scripts/test-lint-a11y.py

@@ -18,7 +18,7 @@ BUILD_ICONS = ROOT / "scripts/build-icons.py"
 MOTION_TEMPLATE = ROOT / "skills/diagram-design/assets/template-motion.html"
 
 VALID_SVG = """\
-<svg xmlns="http://www.w3.org/2000/svg" role="img"
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 800 600" role="img"
      aria-labelledby="fixture-title fixture-desc">
   <title id="fixture-title">Fixture diagram</title>
   <desc id="fixture-desc">Diagram showing a fixture connected to a result.</desc>
@@ -156,6 +156,67 @@ def main() -> int:
             'duplicate accessible-name id="fixture-desc" is not allowed',
             directory,
         )
+        require_failure(
+            "missing-viewbox",
+            VALID_SVG.replace(' viewBox="0 0 800 600"', ""),
+            "diagram <svg> must have a viewBox attribute",
+            directory,
+        )
+        require_failure(
+            "invalid-viewbox",
+            VALID_SVG.replace('viewBox="0 0 800 600"', 'viewBox="0 0 -10 100"'),
+            'viewBox "0 0 -10 100" is not valid (expected "min-x min-y width height" with positive size)',
+            directory,
+        )
+        require_failure(
+            "viewbox-zero-height",
+            VALID_SVG.replace('viewBox="0 0 800 600"', 'viewBox="0 0 800 0"'),
+            'viewBox "0 0 800 0" is not valid (expected "min-x min-y width height" with positive size)',
+            directory,
+        )
+        require_failure(
+            "viewbox-malformed-token",
+            VALID_SVG.replace('viewBox="0 0 800 600"', 'viewBox="0 0 800px 600"'),
+            'viewBox "0 0 800px 600" is not valid (expected "min-x min-y width height" with positive size)',
+            directory,
+        )
+        require_failure(
+            "title-too-long",
+            VALID_SVG.replace("Fixture diagram", "A" * 61),
+            "<title> must be 60 characters or fewer (got 61)",
+            directory,
+        )
+        require_pass(
+            "viewbox-comma-separated",
+            VALID_SVG.replace('viewBox="0 0 800 600"', 'viewBox="0,0,800,600"').replace(
+                "fixture-title", "viewbox-comma-separated-title"
+            ).replace("fixture-desc", "viewbox-comma-separated-desc"),
+            directory,
+        )
+        require_failure(
+            "viewbox-nonfinite-width",
+            VALID_SVG.replace('viewBox="0 0 800 600"', 'viewBox="0 0 inf 600"').replace(
+                "fixture-title", "viewbox-nonfinite-width-title"
+            ).replace("fixture-desc", "viewbox-nonfinite-width-desc"),
+            'viewBox "0 0 inf 600" is not valid (expected "min-x min-y width height" with positive size)',
+            directory,
+        )
+        require_failure(
+            "viewbox-nonfinite-height",
+            VALID_SVG.replace('viewBox="0 0 800 600"', 'viewBox="0 0 800 inf"').replace(
+                "fixture-title", "viewbox-nonfinite-height-title"
+            ).replace("fixture-desc", "viewbox-nonfinite-height-desc"),
+            'viewBox "0 0 800 inf" is not valid (expected "min-x min-y width height" with positive size)',
+            directory,
+        )
+        require_failure(
+            "viewbox-underscore-width",
+            VALID_SVG.replace('viewBox="0 0 800 600"', 'viewBox="0 0 1_000 600"').replace(
+                "fixture-title", "viewbox-underscore-width-title"
+            ).replace("fixture-desc", "viewbox-underscore-width-desc"),
+            'viewBox "0 0 1_000 600" is not valid (expected "min-x min-y width height" with positive size)',
+            directory,
+        )
         require_pass(
             "decorative",
             '<svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true">'