Issue boards: Fix page title after board loaded

The following discussion from !194170 (merged) should be addressed:

• @seggenberger started a discussion: (+3 comments)

  non-blocking, question: @nickleonard @nickbrandt something I noticed is that the page title changes when the page loads, is this intented?

  While loading	Done

Implementation plan

1. Open file: app/assets/javascripts/boards/components/boards_selector.vue

2. Find the watcher (around line 143):

watch: {
  board(newBoard) {
    document.title = newBoard.name;
  },
},

3. Fix and Test: Navigate to any board and verify title shows as "Board Name - Issue Boards" instead of just "Board Name"
4. Expected result: No more title flashing, maintains GitLab's standard "Specific - General" title format