docs: correct GOTOOLCHAIN behavior and harden Go install block

Address the second round of review feedback on #58:

- seictl: the note claimed `go build` fails on a Go 1.25.6 toolchain. With the
  default GOTOOLCHAIN=auto the go command fetches the toolchain go.mod requires,
  so it succeeds; only GOTOOLCHAIN=local or an offline build actually fails.
- node: drop the per-release Go enumeration that duplicated go.mod and needed an
  edit every minor release; keep the durable "check the tag's go.mod" pointer.
- node: hoist the Go tarball and SHA256 into variables so a bump is a two-line
  change, and switch wget to curl -fLO to match the sibling install snippets.
- node: note that `rm -rf /usr/local/go` misses package-manager installs, point
  at `which -a go`, and say a failed extract can just be re-run.

Verified against upstream: seictl go.mod is `go 1.26.0` with no toolchain
directive, sei-chain go.mod is 1.25.6 from v6.4.0 (v6.3.0 was 1.24.5), and the
pinned SHA256 matches go.dev's published checksum for go1.25.6.linux-amd64.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: alexander-sei

node/index.mdx

@@ -66,25 +66,31 @@ timedatectl
 You need Go only if you build `seid` from source. The prebuilt binary and Docker
 install paths in the next step do not require it.
 
-`seid` v6.4.0 and later require Go 1.25.6 or later; v6.3.x builds with Go 1.24.5. Check
-the `go.mod` at the release tag you check out
+Current `seid` releases require Go 1.25.6 or later. Check the `go.mod` at the release tag
+you check out
 (e.g. [`v6.6.1`](https://github.com/sei-protocol/sei-chain/blob/v6.6.1/go.mod)) for its
 exact requirement.
 
 ###### Installation Steps
 
 ```bash
-# Check for existing Go installation
+# Check for existing Go installations — more than one entry means another copy
+# may still win on your PATH after this install
+which -a go
 go version
 
-# Download Go 1.25.6
-wget https://go.dev/dl/go1.25.6.linux-amd64.tar.gz
+# Bumping Go? Change these two lines only
+GO_TARBALL=go1.25.6.linux-amd64.tar.gz
+GO_SHA256=f022b6aad78e362bcba9b0b94d09ad58c5a70c6ba3b7582905fababf5fe0181a
 
-# Verify integrity before trusting the archive (go.dev/dl publishes a SHA256 per file),
-# then replace any previous installation — extracting over one leaves stale files behind
-echo "f022b6aad78e362bcba9b0b94d09ad58c5a70c6ba3b7582905fababf5fe0181a  go1.25.6.linux-amd64.tar.gz" | sha256sum -c - \
+curl -fLO https://go.dev/dl/${GO_TARBALL}
+
+# Verify integrity before trusting the archive (go.dev/dl publishes a SHA256 per file
+# at ${GO_TARBALL}.sha256), then replace any previous installation — extracting over
+# one leaves stale files behind
+echo "${GO_SHA256}  ${GO_TARBALL}" | sha256sum -c - \
   && sudo rm -rf /usr/local/go \
-  && sudo tar -C /usr/local -xzf go1.25.6.linux-amd64.tar.gz
+  && sudo tar -C /usr/local -xzf ${GO_TARBALL}
 
 # Add Go to your environment variables
 echo 'export PATH=$PATH:/usr/local/go/bin' >> $HOME/.bashrc
@@ -93,6 +99,16 @@ source $HOME/.bashrc
 # Verify installation
 go version
 ```
+
+<Note>
+  `sudo rm -rf /usr/local/go` is the replacement step [Go's install
+  docs](https://go.dev/doc/install) prescribe, but it only clears a tarball install. A
+  package-manager Go (`/usr/lib/go-*`, Homebrew) survives it and can still shadow
+  `/usr/local/go/bin/go` — if the final `go version` reports the old release,
+  `which -a go` lists every copy on your `PATH`. If the extraction itself fails, the
+  verified tarball is still in your working directory: re-run the `sudo tar` command
+  rather than starting over.
+</Note>
 </Step>
 
 <Step title="Install Sei">

node/seictl.mdx

@@ -108,9 +108,11 @@ If you prefer to build from source or need a specific configuration:
 - [Go 1.26.0 or later](https://go.dev/doc/install). The commands below build `main`, whose requirement is set in [`go.mod`](https://github.com/sei-protocol/seictl/blob/main/go.mod).
 
 <Note>
-  This is newer than the Go version needed to build `seid` (1.25.6). If you installed Go by
-  following the [node setup guide](/node), your toolchain is a minor version too old and
-  `go build` will fail — upgrade to Go 1.26.0 or later, or use a prebuilt binary above.
+  This is newer than the Go version needed to build `seid` (1.25.6), so the toolchain from
+  the [node setup guide](/node) is a minor version behind. Under the default
+  `GOTOOLCHAIN=auto` that still builds: the go command downloads the toolchain `go.mod`
+  asks for. If you've set `GOTOOLCHAIN=local` or build without network access, install Go
+  1.26.0 or later, or use a prebuilt binary above.
 </Note>
 
 #### Build