docs: remove stale build.sh reference from publisher Key Files (#1504)

The Key Files list in `cmd/publisher/README.md` includes a bullet for
`build.sh`, but there is no `build.sh` anywhere in the repo. The
publisher is built with `make publisher`, which runs `go build -o
bin/mcp-publisher ./cmd/publisher` (Makefile), so there is no separate
cross-platform build script.

The other three entries in the same list (`main.go`, `commands/`,
`auth/`) all exist. This removes the stale bullet so the list matches
the actual files in the directory.

cmd/publisher/README.md

@@ -44,4 +44,3 @@ Optional: enables `dns` and `http` methods to sign out-of-process without direct
 - **`main.go`** - CLI setup and command routing
 - **`commands/`** - Command implementations with auto-detection logic
 - **`auth/`** - Authentication provider implementations
-- **`build.sh`** - Cross-platform build script