fix(cc-config): .claude.json sits BESIDE ~/.claude by default, not inside it

The previous commit routed the read through getClaudeHome(), which appends
/.claude when CLAUDE_HOME is unset — pointing the dashboard at
~/.claude/.claude.json, a file the CLI never writes by default. Verified
against the real binary: with CLAUDE_CONFIG_DIR unset the CLI writes
$HOME/.claude.json; with it set, .claude.json sits flat inside that dir.
Branch on CLAUDE_HOME accordingly.

The test now drives a fake claude that writes where the real one does and
asserts getClaudeJsonPath() names that exact file, under both branches —
the previous test only restated the implementation.

server/lib/cc-discovery.js

@@ -29,13 +29,21 @@ function getProjectClaudeDir(cwd) {
 }
 
 function getClaudeJsonPath() {
-  // One root for everything: this file used to resolve from $HOME while the
-  // other 19 read paths derived from getClaudeHome(), and cc-plugin-cli.js's
-  // runClaude() pinned CLAUDE_CONFIG_DIR to getClaudeHome() — which is where
-  // the CLI puts .claude.json. The dashboard read one file and made the CLI
-  // write another, so MCP add/remove was inert. Keep this and runClaude's
-  // env in step; they are the same decision seen from two sides.
-  return path.join(getClaudeHome(), ".claude.json");
+  // NOT path.join(getClaudeHome(), ".claude.json") — verified against the
+  // real `claude` binary, the two CLAUDE_HOME branches behave differently:
+  //   - CLAUDE_HOME set: the CLI's CLAUDE_CONFIG_DIR (pinned to it by
+  //     cc-plugin-cli.js's runClaude()) becomes a $HOME-substitute for both
+  //     `.claude.json` AND the rest of the tree (projects/, settings.json,
+  //     plugins/) — flat inside it, no nested ".claude". Same value
+  //     getClaudeHome() returns in this branch, so the two formulas agree.
+  //   - CLAUDE_HOME unset: runClaude() deliberately leaves CLAUDE_CONFIG_DIR
+  //     unset too, and the CLI's OWN default writes `.claude.json` BESIDE
+  //     `~/.claude`, not inside it — while getClaudeHome()'s unset branch
+  //     appends "/.claude". Delegating to getClaudeHome() here would read
+  //     `~/.claude/.claude.json`, a file the CLI never writes by default.
+  return process.env.CLAUDE_HOME
+    ? path.join(process.env.CLAUDE_HOME, ".claude.json")
+    : path.join(os.homedir(), ".claude.json");
 }
 
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