Change agents and skills fields in plugin.json to array format for Claude Code CLI compatibility (#407)

* Initial plan

* Remove agents string field from plugin.json and handle array format in parser

Claude Code CLI validates `agents` as array-of-strings per its plugin manifest
schema. Our plugin.json files had `"agents": "./agents/"` (a string), which
caused "agents: Invalid input" validation errors on install.

Remove the field from the 3 affected plugin.json files — agents are still
discovered by convention from the `agents/` directory. Also make ParsePluginJson
resilient to both string and array formats for forward-compatibility.

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

* Remove `agents` string field from plugin.json for Claude Code CLI compatibility

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

* Change agents field to array format in plugin.json, update validator to read array-first with string fallback

Plugin.json files now declare agents as an array of file paths:
  "agents": ["./agents/foo.agent.md", "./agents/bar.agent.md"]

ParsePluginJson reads the array first (preferred, Claude Code schema),
falls back to a string path (legacy). PluginInfo gains an AgentPaths
field. Validator and discovery use the array when present, else fall
back to directory-based convention.

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

* Simplify agents to directory-path array form ["./agents/"], handle directories in array entries

Per Copilot CLI spec, agents field values are "Path(s) to agent directories"
— no need to list individual files. Use ["./agents/"] to mirror how
skills uses "./skills/". Updated validator and discovery to handle both
directory and file entries in the array.

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

* Delete .nuget/nuget.exe

* Apply suggestions from code review

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Convert skills field to array format in plugin.json, update validator to handle both forms

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

* Align AgentPaths null checks to use { Count: > 0 } pattern for consistency

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

* Change `agents` and `skills` fields in plugin.json to array format for Claude Code CLI compatibility

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

* Delete .nuget/nuget.exe

* Consolidate SkillsPath/SkillPaths and AgentsPath/AgentPaths into single array fields

Remove dual string/array fields from PluginInfo. The parser now
normalizes legacy string values into single-element arrays, so all
downstream code uses only SkillPaths and AgentPaths (IReadOnlyList<string>).
This eliminates all array-vs-string fallback branching.

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>
Co-authored-by: Viktor Hofer <viktor.hofer@microsoft.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

plugins/dotnet/plugin.json

@@ -2,6 +2,6 @@
   "name": "dotnet",
   "version": "0.1.0",
   "description": "Common everyday C#/.NET coding skills. Expected to be useful to all .NET developers.",
-  "skills": "./skills/",
+  "skills": ["./skills/"],
   "lspServers": "./lsp.json"
 }