fix(skill-loader): discover skills from .agents/skills/ directory

Add discoverProjectAgentsSkills() for project-level .agents/skills/ and
discoverGlobalAgentsSkills() for ~/.agents/skills/ — matching OpenCode's
native skill discovery paths (https://opencode.ai/docs/skills/).

Updated discoverAllSkills(), discoverSkills(), and createSkillContext()
to include these new sources with correct priority ordering.

Co-authored-by: dtateks <dtateks@users.noreply.github.com>
Closes #1818

src/plugin/skill-context.ts

@@ -12,6 +12,8 @@ import {
   discoverProjectClaudeSkills,
   discoverOpencodeGlobalSkills,
   discoverOpencodeProjectSkills,
+  discoverProjectAgentsSkills,
+  discoverGlobalAgentsSkills,
   mergeSkills,
 } from "../features/opencode-skill-loader"
 import { createBuiltinSkills } from "../features/builtin-skills"
@@ -55,7 +57,7 @@ export async function createSkillContext(args: {
   })
 
   const includeClaudeSkills = pluginConfig.claude_code?.skills !== false
-  const [configSourceSkills, userSkills, globalSkills, projectSkills, opencodeProjectSkills] =
+  const [configSourceSkills, userSkills, globalSkills, projectSkills, opencodeProjectSkills, agentsProjectSkills, agentsGlobalSkills] =
     await Promise.all([
       discoverConfigSourceSkills({
         config: pluginConfig.skills,
@@ -65,15 +67,17 @@ export async function createSkillContext(args: {
       discoverOpencodeGlobalSkills(),
       includeClaudeSkills ? discoverProjectClaudeSkills(directory) : Promise.resolve([]),
       discoverOpencodeProjectSkills(directory),
+      discoverProjectAgentsSkills(directory),
+      discoverGlobalAgentsSkills(),
     ])
 
   const mergedSkills = mergeSkills(
     builtinSkills,
     pluginConfig.skills,
     configSourceSkills,
-    userSkills,
+    [...userSkills, ...agentsGlobalSkills],
     globalSkills,
-    projectSkills,
+    [...projectSkills, ...agentsProjectSkills],
     opencodeProjectSkills,
     { configDir: directory },
   )