feat(research): integrate Context7 MCP as primary source channel

Adds Context7 resolution before websearch for library/framework/API topics,
reducing reliance on web crawling for well-indexed libraries. Falls back to
websearch for unresolved libraries, concept topics, or when the user provides
starting URLs. Subagents are explicitly prohibited from calling Context7 to
prevent tool inheritance from producing duplicate or conflicting summaries.

Includes trigger and output evals for the Context7 path (resolves, fallback,
skipped for non-library topics), stale description and constraint fixes, and a
concrete "sufficient content" threshold.

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

.agents/skills/research/META.md

@@ -1,11 +1,15 @@
 ```yaml
-version: "1.0"
+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 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.
+  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
 ```