fix(mcp): add optional Context7 Authorization header (#1133)

Context7 should mirror `websearch` by only sending auth when
`CONTEXT7_API_KEY` is set.

Change: set bearer auth in `headers` using `CONTEXT7_API_KEY` if said environment variable is set, otherwise leave `headers` to `undefined`.

src/mcp/context7.ts

@@ -2,5 +2,9 @@ export const context7 = {
   type: "remote" as const,
   url: "https://mcp.context7.com/mcp",
   enabled: true,
+  headers: process.env.CONTEXT7_API_KEY
+    ? { Authorization: `Bearer ${process.env.CONTEXT7_API_KEY}` }
+    : undefined,
+  // Disable OAuth auto-detection - Context7 uses API key header, not OAuth
   oauth: false as const,
 }