SpokenPunctuationPass keeps a dictated comma as a word when a determiner opens the noun phrase before it

`SpokenPunctuationPass` refuses a spoken comma that ends a noun phrase opened by a determiner, so a comma the speaker plainly dictated stays a word.

`MentionGuard.isMentioned` is called with `reach: MentionGuard.phraseReach` (3), so a determiner up to three words back makes the mark name a mention. That reach exists for "the trial period" and "the 100 metre dash", where the name heads the noun phrase. It also fires when the name only follows a noun phrase:

```
if the tests pass comma we ship tonight -> comma kept as a word
the cafe by the station comma which opens early ... -> comma kept as a word
pack the charger comma the cable comma and the adapter -> both commas kept as words
```

Measured with `make bakeoff --baselines-only` on the branch for #237: all three fail on rules, Apple and shipping, both before and after that change. They are in the corpus as `spoken-comma-before-a-clause`, `spoken-commas-around-a-clause` and `spoken-commas-in-a-list`.

Why this is not a one-line fix: the same shape is a real mention for a name that heads its phrase, "the 100 metre dash was close", and the word after the name ("was", "we") is a function word in both. Shortening the reach for "comma" alone may be defensible, since "comma" rarely heads a modified noun phrase, but that needs its own corpus cases for the mention side first.

Found while measuring #237; left out of that fix because it moves a different guard.

Locate SpokenPunctuationPass and MentionGuard.isMentioned, then run `make bakeoff --baselines-only` for the three named corpus cases: spoken-comma-before-a-clause, spoken-commas-around-a-clause, and spoken-commas-in-a-list. Read the existing mention examples and add coverage for both rejected commas and valid noun-phrase mentions; done means the comma cases pass without regressing those mentions.

Written by the indexing model from the issue text.