build+docs: bump minimum Go version to 1.25.5

With Go 1.26 now released, this bumps the minimum required Go version
from 1.24.11 to 1.25.5 across all go.mod files and updates the
installation documentation with the correct download links and SHA256
hashes for Go 1.25.5 binaries.

The build system (Dockerfiles, Makefile, CI) was already using Go 1.25.5,
so this change aligns the go.mod minimum version to match.

tools/go.mod

@@ -1,6 +1,6 @@
 module github.com/lightningnetwork/lnd/tools
 
-go 1.24.11
+go 1.25.5
 
 require (
 	4d63.com/gocheckcompilerdirectives v1.3.0 // indirect

tools/linters/go.mod

@@ -1,6 +1,6 @@
 module github.com/lightningnetwork/lnd/tools/linters
 
-go 1.24.11
+go 1.25.5
 
 require (
 	github.com/golangci/plugin-module-register v0.1.1