fix(bookcontent): open commentary at the currently displayed line

[kdroidFilter]

Summary

• Clicking a commentator's header in the commentaries pane now opens its book at the line it links to for the currently displayed base line(s) — e.g. while on Eruvin 33b, clicking רשב״א opens the Rashba at daf 33 — instead of at the book's beginning.
• The target line is resolved in the VM via a new CommentariesUseCase.resolveCommentaryTargetLine, reusing the same paging sources the grid renders so the position matches what is on screen.
• Falls back to opening the book at its start when the commentator has no commentary on those lines.
• Threaded the current LineSelection into the commentaries layout config so the header click carries the base line ids; extended the existing OpenBookByIdInNewTab event with optional baseLineIds (no new event type).

Closes #490

Test plan

• Open a Gemara daf (e.g. Eruvin 33b), select a line, open the commentaries pane.
• Click a commentator header (e.g. רשב״א) → new tab opens at the corresponding daf/line, not page 1.
• Click a commentator that has no link on the current line → book opens at its beginning (fallback).
• Verify behavior in both single-line and multi-line (Ctrl+click) selection.