Re-vendor the shared files from sneak/prompts at 0653579 (closes #52)

Takes .golangci.yml, .dockerignore, .gitignore, .editorconfig, the
workflow and REPO_POLICIES.md from sneak/prompts 0653579, with this
repository's own entries after the shared content. Lint (golangci-lint
v2.14.0) and test are Dockerfile phases that script/lint and script/test
build alone with a new CACHEBUST value, keeping Go's and golangci-lint's
caches; the image build depends on both. make fmt and make fmt-check also
format the markdown with prettier, pinned in yarn.lock. The agent
guidance moves to AGENTS.md. The Go code is fixed for what the new
configuration finds, and the AS and prefix detail reads now return the
rows' error after their loops.

Model: opus-5-5

internal/routewatch/handler.go

@@ -1,6 +1,8 @@
 package routewatch
 
 import (
+	"slices"
+
 	"git.eeqj.de/sneak/routewatch/internal/logger"
 	"git.eeqj.de/sneak/routewatch/internal/ristypes"
 )
@@ -15,10 +17,11 @@ type SimpleHandler struct {
 	callback     func(*ristypes.RISMessage)
 }
 
-// NewSimpleHandler creates a new SimpleHandler that accepts specific message types.
-// The messageTypes parameter specifies which RIS message types this handler will process.
-// If messageTypes is empty, the handler will accept all message types.
-// The callback function is invoked for each message that passes the type filter.
+// NewSimpleHandler creates a new SimpleHandler that accepts specific message
+// types. The messageTypes parameter specifies which RIS message types this
+// handler will process. If messageTypes is empty, the handler will accept all
+// message types. The callback function is invoked for each message that
+// passes the type filter.
 func NewSimpleHandler(
 	logger *logger.Logger,
 	messageTypes []string,
@@ -31,22 +34,17 @@ func NewSimpleHandler(
 	}
 }
 
-// WantsMessage returns true if this handler wants to process messages of the given type.
-// It checks whether messageType is in the handler's configured list of accepted types.
-// If no specific types were configured (empty messageTypes slice), it returns true for all types.
+// WantsMessage returns true if this handler wants to process messages of the
+// given type. It checks whether messageType is in the handler's configured
+// list of accepted types. If no specific types were configured (empty
+// messageTypes slice), it returns true for all types.
 func (h *SimpleHandler) WantsMessage(messageType string) bool {
 	// If no specific types are set, accept all messages
 	if len(h.messageTypes) == 0 {
 		return true
 	}
 
-	for _, t := range h.messageTypes {
-		if t == messageType {
-			return true
-		}
-	}
-
-	return false
+	return slices.Contains(h.messageTypes, messageType)
 }
 
 // HandleMessage processes a RIS message by invoking the configured callback function.