feat(workflows): wire TaskUnit/Orchestrator activities, add k8s deploy manifests

Implements real activity-calling logic in OrchestratorWorkflow and
TaskUnitWorkflow (previously stubs), adds GitDiffActivity, and expands
PlanningActivity's I/O to carry repo path and prior task results.

Adds k8s/ deployment manifests (worker Deployment, orchestrator Job,
Kustomize base) for the poimen-workflows Temporal worker, using a
dedicated Kubernetes namespace `poimen` and Temporal namespace
`poimen-harness` rather than sharing the Temporal server's own
`temporal`/`production` namespaces.

internal/config/config.go

@@ -2,6 +2,7 @@ package config
 
 import (
 	"os"
+	"strings"
 )
 
 // TemporalConfig holds Temporal cluster configuration.
@@ -22,8 +23,8 @@ type AppConfig struct {
 func LoadConfig() (AppConfig, error) {
 	cfg := AppConfig{
 		Temporal: TemporalConfig{
-			HostPort:  getEnvOrDefault("TEMPORAL_HOSTPORT", "127.0.0.1:7233"),
-			Namespace: getEnvOrDefault("TEMPORAL_NAMESPACE", "production"),
+			HostPort:  addDefaultPort(getEnvOrDefault("TEMPORAL_HOSTPORT", "127.0.0.1:7233")),
+			Namespace: getEnvOrDefault("TEMPORAL_NAMESPACE", "poimen-harness"),
 			TLSCert:   os.Getenv("TEMPORAL_TLS_CERT"),
 			TLSKey:    os.Getenv("TEMPORAL_TLS_KEY"),
 		},
@@ -39,3 +40,11 @@ func getEnvOrDefault(key, defaultVal string) string {
 	}
 	return defaultVal
 }
+
+func addDefaultPort(hostPort string) string {
+	// If no port specified, add default port 7233
+	if !strings.Contains(hostPort, ":") {
+		return hostPort + ":7233"
+	}
+	return hostPort
+}