docs(6205): embeddings comments state the reason, not the instance that taught it

Record ids, milestone tags, dated measurements and "used to" stories are
removed; the chunker version list now says what each stamped version
contains. Corrected two comments that said a failed search leaves
report["searched"] absent (it is stamped False first), and pointed the
rule-search docstring at _RULEHINT_BAND in retrieval_pipeline instead of a
tier note in plugin_context that no longer exists. plugin_context's own
dangling "note on tiers" pointer is reworded to match.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/services/plugin_context.py

@@ -1665,9 +1665,9 @@ async def build_write_path_hint(
     # resembles what is being written, noticed at the moment it is relevant
     # rather than by being resident in every session.
     #
-    # EVERY TIER — see the note on tiers near RULEHINT_LIMIT: a rule the
-    # session was told about an hour ago is not a rule in front of the reader
-    # now.
+    # EVERY RULE IS ELIGIBLE, including one already named this session: a
+    # rule the session was told about an hour ago is not a rule in front of
+    # the reader now.
     #
     # The arm itself is `retrieval_pipeline.run_rule_arm`: the band, the
     # fresh/repeat split, the unconditional call row and the fresh-only