admin: install the go.mod-pinned templ, not @latest (#12090)

* admin: install the go.mod-pinned templ, not @latest

install-templ fetched templ@latest, which now emits
templruntime.NewAttributeExpression - a symbol absent from the
runtime pinned in go.mod - so every fresh 'make' regenerated
uncompilable _templ.go files. Install the go.mod version and
reinstall when the binary on PATH reports a different one.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* admin: invoke templ from Go's install dir, not PATH

A templ binary earlier on PATH than GOBIN still shadowed the pinned
compiler after install-templ ran, so generate kept emitting code for
the wrong runtime. Resolve GOBIN (or GOPATH/bin) and call the pinned
binary by absolute path for install checks, generate, watch, and fmt.

* admin: regenerate templ output with the pinned v0.3.1070

The checked-in _templ.go files were stamped v0.3.1020, older than the
go.mod pin. Regenerate so the committed code matches the compiler the
runtime links against.

* admin: resolve templ under the first GOPATH entry

go install drops binaries in the first GOPATH element's bin, so a
multi-element GOPATH left TEMPL pointing at a path that does not exist.
Split on the OS list separator so Windows GOPATHs resolve too.

* admin: install pinned templ before fmt and pattern-rule generates

fmt and a direct %_templ.go rebuild invoked TEMPL without ensuring the
pinned binary exists; an order-only prerequisite keeps the check cheap
without forcing regeneration.

* admin: keep spaced GOPATH/templ paths intact in the Makefile

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

weed/admin/view/components/config_sections_templ.go

@@ -1,6 +1,6 @@
 // Code generated by templ - DO NOT EDIT.
 
-// templ: version: v0.3.1020
+// templ: version: v0.3.1070
 package components
 
 //lint:file-ignore SA4006 This context is only used if a nested component is present.

weed/admin/view/components/form_fields_templ.go

@@ -1,6 +1,6 @@
 // Code generated by templ - DO NOT EDIT.
 
-// templ: version: v0.3.1020
+// templ: version: v0.3.1070
 package components
 
 //lint:file-ignore SA4006 This context is only used if a nested component is present.