feat: wire Infisical secret store into API server and MCP tools

- Wire secretsManager in NewHandler() — instantiate InfisicalBackend
  when OIKOS_INFISICAL_SITE_URL is set (previously always nil)
- Add get_secret, list_secrets, set_secret MCP tools with nil-backend
  graceful degradation
- Add oikos secret get|set|list CLI subcommands for Infisical
- Fix Set() bug: create-before-update so new keys are created;
  add Type: "shared" to Update so it finds the right secret;
  disable SDK cache so Get returns fresh data after Set
- Clean enrollment response: remove fake infisical_client_id/
  infisical_client_secret stubs, store age key in Infisical for real

internal/httpapi/server.go

@@ -28,6 +28,7 @@ import (
 	"github.com/dtoro/oikos/internal/httpapi/gen"
 	mcphandler "github.com/dtoro/oikos/internal/mcp"
 	"github.com/dtoro/oikos/internal/safego"
+	"github.com/dtoro/oikos/internal/secrets"
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
 	"github.com/go-chi/cors"
@@ -59,8 +60,11 @@ type Server struct {
 }
 
 // secretsBackend is a minimal interface for secrets operations used by the
-// HTTP API (enrollment key storage, listing). Compatible with internal/secrets.
+// HTTP API (enrollment key storage, listing, retrieval). Compatible with
+// internal/secrets.Backend. If Infisical is configured, a real backend is
+// wired in; otherwise the field stays nil and all guarded paths are no-ops.
 type secretsBackend interface {
+	Get(ctx context.Context, key string) (string, error)
 	Set(ctx context.Context, key string, value string) error
 	List(ctx context.Context) ([]string, error)
 }
@@ -80,6 +84,23 @@ func NewHandler(ctx context.Context, pool *db.Pool, cfg config.Config) http.Hand
 		sseSubs:   make(map[*sseSubscriber]struct{}),
 	}
 
+	// Wire Infisical backend when configured.
+	if cfg.InfisicalSiteURL != "" {
+		infCfg := secrets.InfisicalConfig{
+			SiteURL:      cfg.InfisicalSiteURL,
+			ClientID:     cfg.InfisicalClientID,
+			ClientSecret: cfg.InfisicalClientSecret,
+			ProjectID:    cfg.InfisicalProjectID,
+			SecretPath:   "/",
+			Env:          cfg.InfisicalEnv,
+		}
+		if infCfg.Env == "" {
+			infCfg.Env = "dev"
+		}
+		s.secretsManager = secrets.NewInfisicalBackend(infCfg)
+		slog.Info("secrets backend wired", "backend", "infisical", "site", cfg.InfisicalSiteURL)
+	}
+
 	// Start background SSE listener, tied to ctx for clean shutdown.
 	// handleNotification (called per-message inside sseListener's loop) has
 	// its own recover for the common case; this outer one covers the
@@ -271,7 +292,7 @@ func NewHandler(ctx context.Context, pool *db.Pool, cfg config.Config) http.Hand
 	if nomosAgentID == uuid.Nil && cfg.NomosAgentSlug != "" {
 		_ = pool.QueryRow(ctx, "SELECT id FROM entities WHERE slug = $1", cfg.NomosAgentSlug).Scan(&nomosAgentID)
 	}
-	r.With(combinedAuth(cfg, false)).Handle("/mcp", mcphandler.NewHandler(pool, cfg.MCPBearerToken, nomosAgentID))
+	r.With(combinedAuth(cfg, false)).Handle("/mcp", mcphandler.NewHandler(pool, cfg.MCPBearerToken, nomosAgentID, s.secretsManager))
 
 	if nomosURL := os.Getenv("NOMOS_PROXY_URL"); nomosURL != "" {
 		target, _ := url.Parse(nomosURL)