Add .mcpb Claude Desktop bundle with zero-config token handling

New scripts/build-mcpb.mjs packs a Claude Desktop extension bundle
(scripts/mcpb-wrapper.mjs + manifest + icon) into dist-mcpb/tiletopia.mcpb.
The wrapper reads the bearer token from %APPDATA% at launch and execs
`npx -y mcp-remote`, so no secrets are baked in and Regenerate keeps
working transparently. Run via `pnpm run build:mcpb`.

McpPanel gets a "Download .mcpb" button linking to the releases page; the
help-overlay tip and README MCP section both lead with the bundle install
path and keep the .mcp.json shim recipe as the Claude Code fallback.

Session-log entry in memory.md covers the design choices, especially why
the wrapper-script approach beat the alternatives (user_config prompt
would defeat one-click; baked-in token would be wrong for everyone else).

package.json

@@ -10,6 +10,7 @@
     "test": "vitest run",
     "test:watch": "vitest",
     "check": "tsc --noEmit",
+    "build:mcpb": "node scripts/build-mcpb.mjs",
     "gen:readme": "node scripts/gen-readme-shortcuts.mjs",
     "tauri": "tauri"
   },