chore: move skills and evals to plugins/bin, remove legacy root configs

Skills and evals migrated from .agents/ to plugins/bin/ plugin directory.
Remove .mcp.json, provider-manifest.sh, and skills-lock.json legacy artifacts.

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

plugins/bin/skills/research/META.md

@@ -0,0 +1,15 @@
+```yaml
+version: "1.1"
+updated: 2026-06-21
+
+when: >-
+  Invoked when the user wants to gather structured reference documentation for a
+  tool, library, or API from MCP documentation indexes or web sources. Typically
+  run before writing a new skill that wraps an external tool, or any time
+  reference files are needed for a topic. Triggered explicitly
+  ("/research <topic> <path>") or implicitly when the user asks to look up,
+  gather, or pull docs for a topic before implementing something.
+
+references:
+  - .agents/skills/context7-mcp/SKILL.md  # context7-mcp — MCP source channel integrated at step 2
+```