docs: v3.27.3 — track Claude Code v2.1.42 + Google Antigravity section

- Claude Code releases: v2.1.41 → v2.1.42 (startup perf, prompt cache, Opus 4.6 effort callout)
- New AI ecosystem section: Google Antigravity agent-first IDE comparison
- Version sync across all docs (3.27.2 → 3.27.3)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

machine-readable/claude-code-releases.yaml

@@ -3,8 +3,8 @@
 # Purpose: Track Claude Code product releases for documentation sync
 # Maintained: Manual updates when new releases are announced
 
-latest: "2.1.41"
-updated: "2026-02-13"
+latest: "2.1.42"
+updated: "2026-02-16"
 
 # ════════════════════════════════════════════════════════════════
 # RELEASES (newest first, condensed highlights only)
@@ -15,6 +15,15 @@ releases:
   # 2.1.x Series (January-February 2026)
   # ─────────────────────────────────────────────────────────────
 
+  - version: "2.1.42"
+    date: "2026-02-14"
+    highlights:
+      - "Optimized startup via deferred Zod schema construction"
+      - "Improved prompt cache hit rate by moving date outside system prompt"
+      - "Opus 4.6 effort callout for eligible users"
+      - "Better error messaging for image dimension limits (suggests `/compact`)"
+    breaking: []
+
   - version: "2.1.41"
     date: "2026-02-13"
     highlights: