feat: add top-level core.go — re-exports DI container API

Users can now:
  import core "forge.lthn.ai/core/go"
  c, _ := core.New(core.WithService(factory))
  svc, _ := core.ServiceFor[*MyService](c, "name")

Re-exports: New, WithService, WithName, WithServiceLock, WithAssets,
ServiceFor, Core, Option, Message, Startable, Stoppable, LocaleProvider,
ServiceRuntime.

Sub-packages imported directly: pkg/mnt, pkg/log, etc.

Co-Authored-By: Virgil <virgil@lethean.io>

core.go

@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: EUPL-1.2
+
+// Package core is the Core framework for Go.
+//
+// Import this package to access the full framework surface:
+//
+//	import core "forge.lthn.ai/core/go"
+//
+//	c, _ := core.New(core.WithService(myFactory))
+//	svc, _ := core.ServiceFor[*MyService](c, "name")
+//
+// Sub-packages provide domain-specific capabilities:
+//
+//	core/pkg/core  — DI container, ServiceRuntime, lifecycle
+//	core/pkg/mnt   — mount operations (embed FS, template extraction)
+//	core/pkg/log   — structured logging (re-exported from go-log)
+//
+// The framework object is designed for zero transitive dependencies.
+// Each pkg/ uses stdlib only.
+package core
+
+import (
+	"forge.lthn.ai/core/go/pkg/core"
+)
+
+// Re-export the DI container API at the top level.
+// This lets users write core.New() instead of core.Core.New().
+
+// Core is the central application container.
+type Core = core.Core
+
+// New creates a new Core instance with the given options.
+var New = core.New
+
+// Option configures a Core instance.
+type Option = core.Option
+
+// WithService registers a service factory.
+var WithService = core.WithService
+
+// WithName registers a named service factory.
+var WithName = core.WithName
+
+// WithServiceLock prevents late service registration.
+var WithServiceLock = core.WithServiceLock
+
+// WithAssets registers an embedded filesystem.
+var WithAssets = core.WithAssets
+
+// ServiceFor retrieves a typed service by name.
+func ServiceFor[T any](c *Core, name string) (T, error) {
+	return core.ServiceFor[T](c, name)
+}
+
+// ServiceRuntime is the base for services with typed options.
+type ServiceRuntime[T any] = core.ServiceRuntime[T]
+
+// NewServiceRuntime creates a ServiceRuntime — use pkg/core.NewServiceRuntime[T] directly.
+// Cannot re-export generic functions at the package level.
+
+// Message is the IPC message type.
+type Message = core.Message
+
+// Startable is implemented by services with startup logic.
+type Startable = core.Startable
+
+// Stoppable is implemented by services with shutdown logic.
+type Stoppable = core.Stoppable
+
+// LocaleProvider is implemented by services that provide locale filesystems.
+type LocaleProvider = core.LocaleProvider