feat(bridge): native-vision skip guard + configurable describe output cap

[diegosouzapw]

Summary

PR-C of the OCR/image-to-text migration series (plan: _tasks/superpowers/plans/2026-08-13-ocr-image-to-text-migration.md; patterns migrated from openclaw-zero-token's vision-skip + configurable describe limits).

• Explicit native-vision skip guard (tests/unit/vision-bridge-native-skip.test.ts): permanent regression test proving that when the target model supports vision natively the bridge leaves messages untouched and makes zero vision-model calls — plus a dedicated Skipping: target model supports vision natively log at the capability early-return (the only production change of C1).
• modalityBridgeVisionMaxChars — configurable cap on the vision model's description output ("raise for detail-heavy OCR tasks, cap for terse contexts"):
  • Schema: z.union([z.literal(0), z.number().int().min(100).max(50000)]).optional() — 0 is the explicit "no cap" sentinel, so an operator can always turn the cap back off (gap caught in review and fixed in-series).
  • Defaults/runtime: visionMaxChars: 0 in MODALITY_BRIDGE_DEFAULTS, maxChars on VisionBridgeRuntimeSettings.
  • Truncation applied at the single site where descriptions become [Image N]: text — cached descriptions are stored raw and re-capped at read time, so changing the cap re-applies to cache hits.
  • Dashboard: numeric field in Modality Bridge → Vision → Advanced (same NumberField pattern as Timeout/Max images; UI pulls 1–99 up to 100, 0 stays 0), i18n keys in en + 42 locales via i18n:sync-ui --translate-markers, docs row in GUARDRAILS.md.

Note for the merger: the mandated i18n sync also back-translated ~7 pre-existing unrelated __MISSING__ markers (thinkingMode* family, mostly in pt.json/zh-TW.json) and deduped a stale block — translation-only churn that pays existing i18n debt and raises the coverage ratchet; no hand edits outside this PR's keys.

Validation (TDD)

• vision-bridge-native-skip 1/1 · vision-bridge-maxchars 5/5 (incl. explicit-0 no-truncation and 50-rejected) · UI modality-bridge-vision-tab 6/6 (asserts the PATCH body carries modalityBridgeVisionMaxChars: 2000; pre-existing cases untouched).
• Canaries green: vision-bridge-mode 4/4, task-aware 5/5, modality-bridge-settings, cc-no-reroute 8/8, settings-schema 2/2, describe-cache 3/3.
• typecheck:core 0 · eslint/prettier clean · check:docs-all 0 · zero __MISSING__ for the new keys across 42 locales.
• Devbox note: running the 3 node:test files in one command trips database is locked (shared temp DATA_DIR across parallel test processes — environmental); each file is green in isolation, and CI shards run them separately.

⚠️ base-red inherited: #9985 (ESLint errors from #10240/#9448 — unrelated to this diff)