feat(cli): install command auto-writes ~/.claude.json MCP entry

The previous flow printed a \`claude mcp add ...\` command and asked
users to paste it. That's 2 steps, a typo surface, and a point of
user dropoff. Replace with direct read-modify-write of ~/.claude.json.

install:
- preflights bun on PATH (clear error + Bun.com link if missing)
- verifies the MCP entry file exists on disk
- reads ~/.claude.json (empty object if absent)
- adds/updates mcpServers.claudemesh with resolved absolute path
- writes back with 0600 perms, creates parent dir if needed
- read-back verification (bails loudly if post-write state is wrong)
- idempotent: re-running returns "unchanged" if entry already matches
- preserves existing mcpServers entries + other top-level config keys

uninstall:
- removes the claudemesh entry if present
- no-ops cleanly when entry or config file doesn't exist
- doesn't touch anything else

Both print a clear post-action hint: "Restart Claude Code to load
the MCP server. Then join a mesh with claudemesh join <invite-link>".

verified locally with HOME=/tmp/fake-home:
- fresh install → ✓ added, config emitted correctly
- re-install → ✓ unchanged (idempotent)
- install alongside existing "other-mcp" entry → both preserved,
  plus unrelated top-level keys kept verbatim
- uninstall → ✓ removed, claudemesh gone, other entries intact
- uninstall again → · not present (no error)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/cli/src/index.ts

@@ -10,7 +10,7 @@
  */
 
 import { startMcpServer } from "./mcp/server";
-import { runInstall } from "./commands/install";
+import { runInstall, runUninstall } from "./commands/install";
 import { runJoin } from "./commands/join";
 import { runList } from "./commands/list";
 import { runLeave } from "./commands/leave";
@@ -22,7 +22,8 @@ Usage:
   claudemesh <command> [args]
 
 Commands:
-  install         Print Claude Code MCP registration instructions
+  install         Register claudemesh as a Claude Code MCP server
+  uninstall       Remove claudemesh MCP server registration
   join <link>     Join a mesh via invite link (ic://join/...)
   list            Show all joined meshes
   leave <slug>    Leave a joined mesh
@@ -47,6 +48,9 @@ async function main(): Promise<void> {
     case "install":
       runInstall();
       return;
+    case "uninstall":
+      runUninstall();
+      return;
     case "join":
       await runJoin(args);
       return;