feat(P1): web foundation — main.go, server.go, HTMX vendored, base+home templates (REQ-040)

Go 1.22 net/http.ServeMux + html/template + http.FileServer for static.
HTMX 2.0.10 vendored as web/static/htmx.min.js (NOT go get; G-006).
base.html layout with nav to all 5 screens. home.html overview.

---ci---
project: oy
phase: 1
milestone: v0.6
status: execute
---/ci---

web/server.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"html/template"
+	"log"
+	"net/http"
+	"os"
+)
+
+func runServer() {
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "8080"
+	}
+
+	tmpl, err := template.ParseGlob("web/templates/*.html")
+	if err != nil {
+		log.Fatalf("parse templates: %v", err)
+	}
+
+	mux := http.NewServeMux()
+
+	mux.HandleFunc("GET /", func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/" {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		if err := tmpl.ExecuteTemplate(w, "home.html", nil); err != nil {
+			log.Printf("render home: %v", err)
+		}
+	})
+
+	mux.Handle("GET /static/", http.StripPrefix("/static/", http.FileServer(http.Dir("web/static"))))
+
+	srv := &http.Server{Addr: ":" + port, Handler: mux}
+	log.Printf("OpenYield web on :%s", port)
+	if err := srv.ListenAndServe(); err != nil {
+		log.Fatalf("server: %v", err)
+	}
+}