docs: use GLOSSARY terms verbatim in sessions

[handlename]

Why this change is necessary

AGENTS.md §11 already binds identifiers, comments and commit messages to GLOSSARY.md, but it says nothing about the sentences a development session is actually made of. An agent can name a CSS class comment-card correctly and, in the same breath, describe it to the user as 「右のパネルのコメント欄」 — and that paraphrase is what lands in the code as rightPanel on the next round. Conversation is where identifiers come from, so it was the one place the vocabulary rule did not reach.

The gap is sharpest when the session is not conducted in English. Nothing in the repository said whether a term should be translated, transliterated, or kept exactly as GLOSSARY.md spells it, so every session decided for itself.

Approach

Extend §11 rather than open a new section, so that AGENTS.md keeps exactly one place that sends a reader to GLOSSARY.md. The rule states that a term is a name and a name is not translated: the sentence around it takes the session's language, the term does not. It names the surfaces it covers — chat, scratch notes, plans, PR and issue bodies, review_reply — so the boundary matches the one §11 already draws for commit messages, and it notes that the wire-format exception below it travels with the rule.

A Bad/Good pair set in a Japanese session shows the intended shape, since that is the case the rule exists for. The example stays in Japanese deliberately: translating it into English would leave nothing to illustrate. That is the one considered deviation from §1.

Scope

Deliberately out of scope:

• Mechanical enforcement (hooks, lint, CI) — this is documentation only.
• skills/review-doc/SKILL.md — the rule addresses contributors to reviewer, not people using it.
• How the agent should react when the user uses a different word; only what the agent writes is governed.
• What to call a concept that has no glossary term yet mid-conversation. §11's existing "a thing with no term yet needs a term first" continues to cover code.
• GLOSSARY.md itself is unchanged.

Review Points

• Whether §11 is the right home, or whether this belongs next to §1 as a language policy.
• Whether a Japanese Bad/Good example is acceptable inside an English document, given §1.
• Whether the listed surfaces — PR and issue bodies in particular — draw the boundary in the right place.