Fix canvas description for v3 summaries and language-tagged v2 values - #4617

The "Current item" section of the information panel never shows the summary of a Presentation 3 canvas, and a language-tagged Presentation 2 canvas description shows up as [object Object].

getCanvasDescription in src/state/selectors/canvases.js returned canvas.getProperty('description') as-is. Presentation 3 renamed that property to summary, and the spec says clients SHOULD render summary on a Canvas (3.0 § summary). So for v3 canvases the selector always returns undefined. For example, both canvases in https://iiif-test.github.io/March2025/manifests/manifest.json have a summary that is not displayed. In v2 the value can also be a language-tagged object or an array of them:

"description": [
  { "@value": "A description of the canvas", "@language": "en" },
  { "@value": "Une description du canevas", "@language": "fr" }
]

That value reaches SanitizedHtml unparsed, and DOMPurify turns it into the string [object Object],[object Object].

The selector now reads summary and falls back to description. It then picks the value for the current locale with PropertyValue.parse(...).getValue(locale), the same way the manifest summary is handled (#3633, #3780). It uses the same getManifestLocale as getCanvasLabel and getCanvasMetadata, so it also follows the locale picker. Plain string descriptions come back unchanged.

I added tests to __tests__/src/selectors/canvases.test.js for a v3 summary, a localized v2 description, and the two empty cases. I ran that file under Node 22 with a minimal jest-compatible runner against manifesto.js 4.3.5 and reselect 5.2.0. On main, the v3 and v2 cases fail: one returns undefined and the other returns the raw array. With this change all 26 tests in the file pass. I did not run lint, prettier or the full vitest suite locally.

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