claude-code: load MCP config via plugin dir

Claude Code rejects `--mcp-config` once the Home Manager wrapper injects
it around subcommands, which breaks commands like `claude mcp list`.
Claude Code 2.1.76 fixed `--plugin-dir` so it no longer consumes
following subcommands, so use that path for the generated MCP config
instead.

Generate a plugin directory with a manifest and `.mcp.json`, wrap
`claude` with `--plugin-dir` before user arguments, and snapshot that
wrapper directly in the tests. Keep the existing LSP support in the
generated plugin directory as well, and add coverage for the combined
MCP+LSP case plus the MCP integration merge path.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

tests/modules/programs/claude-code/expected-mcp-plugin.json

@@ -0,0 +1,36 @@
+{
+  "mcpServers": {
+    "customTransport": {
+      "customOption": "value",
+      "timeout": 5000,
+      "type": "websocket",
+      "url": "wss://example.com/mcp"
+    },
+    "database": {
+      "args": [
+        "-y",
+        "@bytebase/dbhub",
+        "--dsn",
+        "postgresql://user:pass@localhost:5432/db"
+      ],
+      "command": "npx",
+      "env": {
+        "DATABASE_URL": "postgresql://user:pass@localhost:5432/db"
+      },
+      "type": "stdio"
+    },
+    "filesystem": {
+      "args": [
+        "-y",
+        "@modelcontextprotocol/server-filesystem",
+        "/tmp"
+      ],
+      "command": "npx",
+      "type": "stdio"
+    },
+    "github": {
+      "type": "http",
+      "url": "https://api.githubcopilot.com/mcp/"
+    }
+  }
+}