feat(kyberforge): add skill-improve skill to factory workflow

Applies evidence-based improvements to existing skills using signals
from grill sessions, audit reports, eval failures, and inline feedback.
Groups signals by root cause before editing to avoid per-symptom patching.
Hands off to /skill-audit on completion.

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

plugins/kyberforge/skills/skill-improve/README.md

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+# skill-improve
+
+Apply evidence-based improvements to an existing skill using signals from the current session.
+
+## What it does
+
+Takes an existing skill directory and one or more improvement signals — grill output, audit findings, eval failures, human feedback, or inline session context — and applies targeted edits to the skill files. Groups signals by root cause before editing to avoid per-symptom patching. Hands off to `/skill-audit` when done.
+
+## Before you start
+
+Have at least one improvement signal ready: a grill session output, `/skill-audit` report, eval results, feedback.json, or inline feedback describing what went wrong. If you have no signals and want a blind review, use `/skill-audit` instead.
+
+## Usage
+
+```
+/skill-improve
+```
+
+Provide the skill directory path and any signal files in the conversation. The skill gathers signals from context — you don't need to paste them in a specific format.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `SKILL.md` | Skill instructions for agents |