1.8.1

v1.8.1: context-gate the glow — don't link a common word where it doesn't fit

The inline glow linked any exact title match, so "analysis" in a security note glowed
the unrelated math "Analysis" note. Gate each glow (and Link-all / auto-link) by
whether the target fits the active note's CONTEXT, via IndexStore.glowAllowed:

• Content-rich target: keep only when its centered (topical) similarity to the
  active note clears GLOW_CONTEXT_FLOOR (0.15) — reuses the 1.8.0 mean-centering, so
  an off-topic note scores ~0 and is dropped.
• Empty stub target: it carries no topic to judge (the title may be an ambiguous
  word), so glow only when there's an explicit structural tie — a link either
  direction or a shared tag. An isolated empty stub (bare "Analysis") has none, so it
  no longer glows off-topic.
  Wired via glowBridge.contextGate (set from main.ts), checked in buildGlow and
  detectMentions after resolve. Verified live: "analysis" no longer underlines in the
  security note (its math target is an isolated empty stub). Note: this also gates other
  isolated empty stubs (e.g. an empty "LLM" note) until they gain content or a link —
  inherent, since an empty note's topic can't be inferred; it self-heals as notes mature.