docs(i18n): resolve R1 vs R8/§7 contradiction on proactive translation

R1 instructed agents to "translate the newly added keys in every locale"
right after syncing, while R8 and §7 make [TODO: Translate] placeholders
the sanctioned end state during feature development until the feature
owner explicitly asks for translations. Reword R1 and the AGENTS.md
Localization section to say stop after syncing and never translate
proactively.

docs/i18n-translation-guidelines.md

@@ -23,7 +23,9 @@ Locales: `en`, `zh-CN`, `zh-TW`, `ja`, `ko`, `fr`, `de`, `es`, `ru`, `he` (RTL).
   same nested key set. `tests/i18n/test_i18n.py` enforces this.
 - When a new UI string is added to `en.json`, run
   `python scripts/sync_translation_keys.py` (adds the missing keys to all locales with
-  placeholder copies), then translate the newly added keys in every locale.
+  `[TODO: Translate]` placeholder copies) — **then stop**. Do NOT translate proactively:
+  placeholders are the expected end state during feature development, and translations are
+  filled in only when the feature owner explicitly asks (workflow details in §7).
 - Never reorder, re-indent, or reformat a locale file "for tidiness". The sync script
   preserves formatting; manual reformatting creates noisy diffs.