fix(skills): use directory param instead of process.cwd() for project skill discovery

Project-level skills (.opencode/skills/ and .claude/skills/) were not
discovered in desktop app environments because the discover functions
hardcoded process.cwd() to resolve project paths. In desktop apps,
process.cwd() points to the app installation directory rather than the
user's project directory.

Add optional directory parameter to all project-level skill discovery
functions and thread ctx.directory from the plugin context through the
entire skill loading pipeline. Falls back to process.cwd() when
directory is not provided, preserving CLI compatibility.

src/plugin/skill-context.ts

@@ -63,8 +63,8 @@ export async function createSkillContext(args: {
       }),
       includeClaudeSkills ? discoverUserClaudeSkills() : Promise.resolve([]),
       discoverOpencodeGlobalSkills(),
-      includeClaudeSkills ? discoverProjectClaudeSkills() : Promise.resolve([]),
-      discoverOpencodeProjectSkills(),
+      includeClaudeSkills ? discoverProjectClaudeSkills(directory) : Promise.resolve([]),
+      discoverOpencodeProjectSkills(directory),
     ])
 
   const mergedSkills = mergeSkills(