chore: migrate SynapseML skills to Copilot path (#2559)

## Summary
Move the remaining SynapseML repo skill from `.agents/skills/` to `.github/skills/` so Copilot CLI can discover all repo-versioned skills from the documented project-skill path. Add README pointers under `.agents/` for tools or agents that inspect the older convention.

## Prompting Intent
The engineer asked to migrate everything to the correct Copilot CLI path and suggested keeping a generic agents pointer. The goal was to make existing skills discoverable by Copilot while avoiding future confusion about `.agents/skills`.

## Linked Sources
- User request in current session: migrate everything to the correct path for Copilot CLI and keep a generic agents pointer.
- Skill location reference: /home/brwals/.copilot/installed-plugins/copilot-toolkit-marketplace/common/skills/create-skill/references/REFERENCE.md
- Prior merged skill PR: #2558

## Rationale
`.github/skills/<name>/` is the documented Copilot CLI project-skill location. Keeping only README pointers under `.agents/` preserves a breadcrumb for other agent conventions without leaving duplicate or stale `SKILL.md` files in a path Copilot CLI may not load.

Author: BrendanWalsh

.agents/README.md

@@ -0,0 +1,7 @@
+# Agent configuration
+
+Copilot CLI discovers project skills from `.github/skills/<skill-name>/`.
+
+Do not add `SKILL.md` files under `.agents/skills/`. Keep repo-versioned skills in `.github/skills/` so Copilot CLI can load them consistently.
+
+This directory remains only as a compatibility pointer for agents or tools that inspect `.agents`.

.agents/skills/README.md

@@ -0,0 +1,10 @@
+# Skills moved
+
+Repo-versioned skills for Copilot CLI live in `.github/skills/`.
+
+Use these paths instead:
+
+- `.github/skills/code-review/`
+- `.github/skills/synapseml-local-setup/`
+
+Do not add `SKILL.md` files in this directory.

.agents/skills/code-review/SKILL.md .github/skills/code-review/SKILL.md.agents/skills/code-review/SKILL.md renamed to .github/skills/code-review/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: code-review
-description: Quick review checklist for python and scala code changes before callings it done.
+description: Review SynapseML Python and Scala code changes. Use before finalizing PR reviews or implementation changes to check security, compatibility, style, generated code, and targeted tests.
 ---
 
 # Code Review
@@ -21,8 +21,8 @@ Use this skill when reviewing SynapseML changes.
 Apply when changes touch serialization, I/O, network, or authentication code.
 
 ### Deserialization (CWE-502)
-- [ ] No raw `ObjectInputStream.readObject()` — use `SafeObjectInputStream` with an allowlist
-- [ ] `resolveClass` allowlist validates array component types — never allowlist the `[` prefix
+- [ ] No raw `ObjectInputStream.readObject()`: use `SafeObjectInputStream` with an allowlist
+- [ ] `resolveClass` allowlist validates array component types. Never allowlist the `[` prefix
       directly; array handling must extract and validate the component class name
 - [ ] `resolveProxyClass` is overridden to block or validate dynamic proxy interfaces
 - [ ] Allowlist uses package-prefix matching, not blocklisting
@@ -46,7 +46,7 @@ Apply when changes modify public classes, traits, or companion objects.
 
 ### Binary Compatibility (JVM)
 - [ ] No method signature changes on existing public methods (default parameters
-      generate synthetic bridges — use explicit overloads instead)
+      generate synthetic bridges; use explicit overloads instead)
 - [ ] No removed or renamed public classes, traits, or objects
 - [ ] Companion object `extends DefaultParamsReadable[T]` preserved if it existed
 
@@ -61,7 +61,7 @@ Apply when changes modify public classes, traits, or companion objects.
 - [ ] `Wrappable` trait mixed in if the class needs a Python wrapper
 - [ ] `SynapseMLLogging` trait mixed in; `logClass()` called in constructor
 - [ ] No wildcard imports where explicit imports suffice (`java.io._` → named imports)
-- [ ] No RDD API usage — DataFrame/Dataset only
+- [ ] No RDD API usage. Use DataFrame/Dataset only
 - [ ] Lines ≤ 120 chars, files ≤ 800 lines
 
 ## Python Checklist