fix(claude): track claude-plugin/.mcp.json so the embed compiles from a clean checkout

.gitignore ignores .mcp.json globally with a negation only for
codex-plugin; claude-plugin/.mcp.json was therefore untracked, so
include_str!("../../claude-plugin/.mcp.json") in src/agents/claude.rs
failed to compile on a fresh clone (CI). Add the negation and commit
the file (byte-identical to codex-plugin/.mcp.json).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: ScriptedAlchemy

.gitignore

@@ -4,6 +4,7 @@
 .tracedecay
 .mcp.json
 !codex-plugin/.mcp.json
+!claude-plugin/.mcp.json
 .claude/
 .cursor/
 docs/superpowers

claude-plugin/.mcp.json

@@ -0,0 +1,14 @@
+{
+  "mcpServers": {
+    "tracedecay": {
+      "type": "stdio",
+      "command": "tracedecay",
+      "args": [
+        "serve"
+      ],
+      "env": {
+        "TRACEDECAY_ENABLE_GLOBAL_DB": "1"
+      }
+    }
+  }
+}