Re-vendor the canonical files from sneak/prompts at dd4027b (closes #112)

The shared files are fetched from sneak/prompts dd4027b, with this
repository's own entries after the shared content in .gitignore,
.editorconfig and .dockerignore.

Lint and tests are Dockerfile phases (golangci-lint v2.14.0, Debian Go
1.24.13) that the build stage depends on, and the Makefile targets call
the script/ entrypoints. make fmt also formats Markdown with prettier.

Fixes for the new lint findings: the auth cookie is always Secure, an
IRC connection's relay goroutine stops when the connection closes, and
repeated strings are constants. neoirc-cli treats a plain-HTTP server on
localhost or a loopback address as secure, so local use keeps its session.

Whether the 60-second test cap covers building the test phase is open
on sneak/prompts issue 113.

Model: opus-5-5

internal/ircserver/commands.go

@@ -159,9 +159,7 @@ func (c *Conn) handleJoin(
 		return
 	}
 
-	channels := strings.Split(msg.Params[0], ",")
-
-	for _, chanName := range channels {
+	for chanName := range strings.SplitSeq(msg.Params[0], ",") {
 		chanName = strings.TrimSpace(chanName)
 
 		if !strings.HasPrefix(chanName, "#") {
@@ -305,9 +303,7 @@ func (c *Conn) handlePart(
 		reason = msg.Params[1]
 	}
 
-	channels := strings.Split(msg.Params[0], ",")
-
-	for _, ch := range channels {
+	for ch := range strings.SplitSeq(msg.Params[0], ",") {
 		ch = strings.TrimSpace(ch)
 		c.partChannel(ctx, ch, reason)
 	}
@@ -619,8 +615,8 @@ func (c *Conn) applyChannelModes(
 ) {
 	adding := true
 	argIdx := 0
-	applied := ""
-	appliedArgs := ""
+
+	var applied, appliedArgs strings.Builder
 
 	for _, modeChar := range modeStr {
 		var res modeResult
@@ -672,16 +668,13 @@ func (c *Conn) applyChannelModes(
 		argIdx += res.consumed
 
 		if !res.skip {
-			applied += res.applied
-			appliedArgs += res.appliedArgs
+			applied.WriteString(res.applied)
+			appliedArgs.WriteString(res.appliedArgs)
 		}
 	}
 
-	if applied != "" {
-		modeReply := applied
-		if appliedArgs != "" {
-			modeReply += appliedArgs
-		}
+	if applied.Len() > 0 {
+		modeReply := applied.String() + appliedArgs.String()
 
 		c.send(FormatMessage(
 			c.hostmask(), "MODE", channel, modeReply,