fix: restore non-breaking-space literal lost in transcription

The previous commit accidentally normalized the non-breaking space
(U+00A0) in _normalize_unicode's replace() call to a regular space
during a copy/paste, turning that replace() into a no-op. Use an
explicit   escape instead of the literal character so it can't
be silently corrupted again.

bcc_core.py

@@ -499,7 +499,7 @@ def _normalize_unicode(text: str, notes: list[str]) -> str:
     out = text
     for junk in _JUNK_CHARS:
         out = out.replace(junk, "")
-    out = out.replace(" ", " ")  # non-breaking space
+    out = out.replace(" ", " ")  # non-breaking space
     for smart, ascii_q in _QUOTE_MAP.items():
         out = out.replace(smart, ascii_q)
     if out != text: