Read the architecture at run time, not via a Buildarch ldflag (closes #164)

CONVENTIONS.md no longer passes the build architecture in through the
Makefile. The Buildarch variable, globals field and BUILDARCH Makefile
lines are removed from every example, and the logger's Identify example
logs "arch", runtime.GOARCH, as internal/logger already does. Wording
matches the HTTP server conventions in sneak/prompts.

Model: opus-5-5

CONVENTIONS.md

@@ -112,15 +112,13 @@ import (
 )
 
 var (
-    Appname   string = "CHANGEME"
-    Version   string
-    Buildarch string
+    Appname string = "CHANGEME"
+    Version string
 )
 
 func main() {
     globals.Appname = Appname
     globals.Version = Version
-    globals.Buildarch = Buildarch
 
     fx.New(
         fx.Provide(
@@ -859,7 +857,7 @@ func (l *Logger) Identify() {
     l.log.Info("starting",
         "appname", l.params.Globals.Appname,
         "version", l.params.Globals.Version,
-        "buildarch", l.params.Globals.Buildarch,
+        "arch", runtime.GOARCH,
     )
 }
 ```
@@ -979,23 +977,20 @@ import "go.uber.org/fx"
 
 // Package-level variables (set from main)
 var (
-    Appname   string
-    Version   string
-    Buildarch string
+    Appname string
+    Version string
 )
 
 // Struct for DI
 type Globals struct {
-    Appname   string
-    Version   string
-    Buildarch string
+    Appname string
+    Version string
 }
 
 func New(lc fx.Lifecycle) (*Globals, error) {
     n := &Globals{
-        Appname:   Appname,
-        Buildarch: Buildarch,
-        Version:   Version,
+        Appname: Appname,
+        Version: Version,
     }
     return n, nil
 }
@@ -1006,15 +1001,13 @@ func New(lc fx.Lifecycle) (*Globals, error) {
 ```go
 // cmd/httpd/main.go
 var (
-    Appname   string = "CHANGEME"  // Default, overridden by build
-    Version   string               // Set at build time
-    Buildarch string               // Set at build time
+    Appname string = "CHANGEME"  // Default, overridden by build
+    Version string               // Set at build time
 )
 
 func main() {
     globals.Appname = Appname
     globals.Version = Version
-    globals.Buildarch = Buildarch
     // ...
 }
 ```
@@ -1025,10 +1018,9 @@ Use ldflags to inject version information at build time:
 
 ```makefile
 VERSION := $(shell git describe --tags --always)
-BUILDARCH := $(shell go env GOARCH)
 
 build:
-    go build -ldflags "-X main.Version=$(VERSION) -X main.Buildarch=$(BUILDARCH)" ./cmd/httpd
+    go build -ldflags "-X main.Version=$(VERSION)" ./cmd/httpd
 ```
 
 ---