dockerimg: remove configurability from open browser request

Innie is untrusted, so we can't let it provide a url to open (duh).
There's a chicken-and-egg problem here: we need to start the git
server before launching the container, but we need the container
port information to store the ps1URL on the git server.
Solve it with a little sync/atomic. There's a logical race here,
but if we lose the race, the behavior is that nothing happens,
at which point the user tries again and it works.
Good enough for now.

Co-Authored-By: sketch <hello@sketch.dev>
diff --git a/dockerimg/githttp.go b/dockerimg/githttp.go
index 6270838..7ce5f40 100644
--- a/dockerimg/githttp.go
+++ b/dockerimg/githttp.go
@@ -3,7 +3,6 @@
 import (
 	"crypto/subtle"
 	"fmt"
-	"io"
 	"log/slog"
 	"net/http"
 	"net/http/cgi"
@@ -15,7 +14,7 @@
 type gitHTTP struct {
 	gitRepoRoot string
 	pass        []byte
-	browserC    chan string // browser launch requests
+	browserC    chan bool // browser launch requests
 }
 
 func (g *gitHTTP) ServeHTTP(w http.ResponseWriter, r *http.Request) {
@@ -54,20 +53,11 @@
 			http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
 			return
 		}
-		body, err := io.ReadAll(r.Body)
-		if err != nil {
-			http.Error(w, "Failed to read request body: "+err.Error(), http.StatusBadRequest)
-			return
-		}
 		defer r.Body.Close()
-		url := strings.TrimSpace(string(body))
-		if len(url) == 0 {
-			http.Error(w, "URL cannot be empty", http.StatusBadRequest)
-			return
-		}
+
 		select {
-		case g.browserC <- string(url):
-			slog.InfoContext(r.Context(), "open browser", "url", url)
+		case g.browserC <- true:
+			slog.InfoContext(r.Context(), "open browser requested")
 			w.WriteHeader(http.StatusOK)
 		default:
 			http.Error(w, "Too many browser launch requests", http.StatusTooManyRequests)