ANG-014: Notebook scope picker, focus mode, confidence filter & graph design

[yugalkaushik]

• Pick which notebooks appear in the graph: all, current, or selected.
• Focus mode dims everything outside a note's neighbourhood.
• Confidence slider hides low-confidence semantic edges.
• Layout switcher (fCoSE / Hierarchical), community grouping and category filter.
• LLM labels carry over across notebook switches.
• Popular tags link via a capped ring instead of being dropped.
• Notes edited mid-labelling no longer miss their labels, scope-change error fixed.