feat: generate translator credits offline from the committed file

Makes docs/changelog/translators.json self-sufficient so a release no longer
needs to re-query Crowdin:

- sinceLastTag entries now carry each translator's languages ({user, languages}),
  recorded by the --seed run.
- Default mode (no flags) is offline: it generates the "## Translations" block
  straight from the committed file — reading sinceLastTag, grouping by the stored
  languages, and resolving npubs via the mappings registry. No token, no network.
- --seed/--raw remain the online paths (CI seeding / debugging). curl + git +
  credentials are only required there; the offline path needs just jq.

RELEASE_OPS now points at the tokenless `scripts/translators.sh` for the
changelog credits.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FWQWVdWLAwBUBX2gJ55y6b

docs/changelog/translators.json

@@ -9,9 +9,9 @@
     "  matches the Crowdin user id.",
     "",
     "sinceLastTag: a rolling snapshot of who has translated since the last release",
-    "  tag. Refreshed on every --seed run; do not hand-edit. At release time the",
-    "  changelog '## Translations' block is generated from this window and",
-    "  resolved to npubs via mappings (anyone still blank is flagged UNMAPPED).",
+    "  tag. Each entry is { user, languages }. Refreshed on every --seed run; do",
+    "  not hand-edit. The changelog '## Translations' block is generated offline",
+    "  from this list and resolved to npubs via mappings (blanks flagged UNMAPPED).",
     "",
     "Example mapping (replace with a real Crowdin username):",
     "  \"vitorpamplona\": \"npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z\""