🤖 feat: #3623308 Open a page's own translation overview from Translate

Makes the Drupal-side entry points land where the translator needs to be, instead of the full dashboard. Canvas-side entry points (language dropdown, sidebar) need Canvas changes and are out of scope; see the issue.

Changes

• Translate operation and tab (/page/{id}/translations) now open the page's own overview in the extension, not the dashboard. Works with language prefixes too.
• Per-page overview (/canvas/app/canvas_translate/page/{id}): every language of the page with its status and completion, each linking into the editor.
• Translation rows in listings (e.g. the pages view) lead with Edit translation, opening that language in the editor. Core's Edit on those rows is relabelled Edit original, since the Canvas editor always opens the source. Original rows are unchanged; "Edit translation" requires translate canvas content and update access.
• The items endpoint accepts ?id= to return a single page (used by the overview).

Testing

• Kernel: 35 tests pass, including new coverage for the redirect, the ?id= filter and the row operations.
• E2E: new entry-points.spec.ts (Translate → overview → editor); full suite passes.
• Specs updated (content-translation), openspec validate --specs passes. dist rebuilt.

Manual: enable a second language, open /admin/content/pages, use Translate on a page, and Edit translation on a translation's row.

Out of scope

• The editor's "All pages" button still goes to the dashboard (a breadcrumb back to the page overview could be a follow-up).
• No per-page "Review translations" button; publishing works as before.

Closes #3623308