Count the tags this rule would have cost, rather than guessing at it

The module doc said an extractor keyed on string literals would "lose six
genuine tags to save two false ones". The six is right — `schema.rs` carries
that many `-- TRACES:` lines inside Rust literals — but the two undercounted
the false ones, which were R1 twice, FR-CAT-1 twice, FR-CAT-2, NFR-P1, one in
`gestures.rs` and two emitted by `dr-pipeline/build.rs`. The comparison it was
drawing does not need a number on that side to hold.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tools/traceability/src/lib.rs

@@ -28,11 +28,10 @@
 //! reported implemented on the strength of two string literals in a unit test.
 //!
 //! 3. **A tag is a comment whose first word is `TRACES:`**, not a line in which
-//!    the string appears. This is a rule about position
-//!    rather than about string literals, because `schema.rs` writes real tags
-//!    inside string literals — the SQL it embeds is commented with `--` — and
-//!    an extractor that refused those would lose six genuine tags to save two
-//!    false ones.
+//!    the string appears. See `tag_body`. It is a rule about position rather
+//!    than about string literals, because `schema.rs` writes six real tags
+//!    *inside* string literals — the SQL it embeds is commented with `--` — so
+//!    an extractor that refused string literals would lose more than it saved.
 
 use std::collections::{BTreeMap, BTreeSet};
 use std::path::{Path, PathBuf};