feat(skill): implement tiered architecture (v3.0.0)

.agent/rules/humanizer.md

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+# Humanizer Rule
+
+When writing text (especially Markdown/documentation), avoid these common AI-generated patterns:
+
+- **Inflation**: Avoid "stands as a testament", "pivotal moment", "vital role".
+- **-ing overloading**: Avoid "symbolizing X, reflecting Y, and showcasing Z".
+- **AI Vocabulary**: Avoid "delve", "fostering", "tapestry", "rich/vibrant", "landscape".
+- **Copula Avoidance**: Use "is/are" instead of "serves as", "functions as", "stands as".
+- **Structure**: Avoid "In conclusion", "Great question!", "I hope this helps!".
+
+Goal: Write naturally, with specific facts and opinions, not generic fluff.

.agent/skills/humanizer/README.md

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+# Humanizer Antigravity Skill (Adapter)
+
+## Install (Workspace)
+
+Copy this folder into your workspace skill directory:
+
+- `<workspace>/.agent/skills/humanizer/`
+
+## Files
+
+- `SKILL.md` (required by Antigravity)
+
+## Notes
+
+- The canonical rules live in the repo `SKILL.md`.
+- Update adapter metadata in this skill when syncing versions.