fix(viewer): migrate to @nextcloud/viewer for Nextcloud 36

[AndyScherzinger]

Closes #353

Mind maps no longer open on Nextcloud 36. Two independent problems cause it, fixed in separate commits:

• Viewer template returns a 500 — templates/viewer.php used \OC::$server[...], and array access on the server container is gone in 36 (Cannot use object of type OC\Server as array). It now uses OCP\Server::get().
• The handler is never registered — feat(viewer): drop the bundled viewer app for @nextcloud/viewer server#63954 removed the viewer app: LoadViewer is no longer dispatched, and OCA.Viewer.registerHandler() / setRootElement() no longer exist.

Changes for the second part:

• Register the handler with @nextcloud/viewer (^2.0.0-beta.18) from an init script loaded on BeforeTemplateRenderedEvent.
• src/views/MindMap.js is now a native custom element rendering the editor iframe, instead of a Vue 2 component built on the viewer mixin.
• The iframe closes the viewer through OCA.FilesMindMap.close() → getViewer().close().
• The edit file action is only registered on 32. Since @nextcloud/files 4 passes a context object to enabled()/exec(), it was never enabled on 33+ anyway; the viewer now registers the actions for its handlers itself.
• max-version raised to 36.
• The init script only holds the handler registration and the element; the editor logic (mindmap.js, with dialogs, axios and jszip) loads when a mind map is first shown, and the 32-only file action loads from its own chunk on 32 only. What every page loads goes from 1062 kB (301 kB gzip) to 169 kB (61 kB gzip), most of it the @nextcloud/viewer entry itself.

Found while testing on 32:

• Lazy chunks failed to load — the custom renderBuiltUrl in vite.config.ts emitted a bare OC.filePath(), which a minified top-level function OC in the bundle shadows (OC.filePath is not a function). This only surfaces where this app's copy of the viewer is the one mounted (no newer copy on the page, e.g. 32). Dropped the override; @nextcloud/vite-config already emits window.OC.filePath().
• The error toast was handed the Error object and threw, hiding the real error.
• public.js and LoadPublicViewerListener are removed: on 32, 34 and 36 the public share page is rendered by the Files app and opens single-file shares through the default file action, so the #files-public-content container it waited for does not exist on any supported version.
• css/style.css is removed, with LoadAdditionalListener that only added it to Files, its link in the editor iframe, and the template creator's icon-mindmap fallback. None of its rules apply on 32+: the #body-public rules styled that old share page, .ie targeted Internet Explorer, nothing renders #mmframe, and icon-mindmap was only used without setIconSvgInline(), which exists since 29.

Testing

Tested with a browser on Nextcloud 36 (master), 34.0.4 (viewer 7.0.0-dev from stable34) and 32.0.15 (viewer 5.0.0):

	32	34	36
Open from Files	✅	✅	✅
Edit and save	✅	✅	✅
Open public link share	✅	✅	✅

Vitest suite passes. The table was run with @nextcloud/viewer 2.0.0-beta.14; 32 and 36 were re-run after the init script split. After the bump to 2.0.0-beta.18, 36 was re-run (open, save, public share); there this app's copy is elected over the server's 2.0.0-beta.15, so it exercises the bundled viewer and its styles. 32 and 34 were not re-run on beta.18. On 32 and 34 the old viewer app keeps its OCA.Viewer global while the library registry only holds this handler, so both coexist: @nextcloud/viewer only uses window._nc_viewer_scope, never touches OCA.Viewer, and no default handlers are registered. 33 and 35 not tested separately.

Notes

• With 2.0.0-beta.17+ the default theme follows the user's theme, but on a light theme the viewer header title stays light (rgb(235, 235, 235) on white), so it is barely readable. The viewer's CSS is bundled and applied; its header rules only cover the non-default themes, so this looks like a library issue rather than this app.
• src/__tests__/MindMap.spec.js is replaced by mindmapElement.spec.js. Besides testing the removed Vue component, it collided with mindmap.spec.js on case-insensitive filesystems.

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI (N/A)