feat: add llm.txt — agent entry point for CoreGO framework

Standard llm.txt with package layout, key types, service pattern.
Points to CLAUDE.md and docs/RFC.md for full specs.

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

llm.txt

@@ -0,0 +1,41 @@
+# core/go — CoreGO DI Framework
+
+> dappco.re/go/core — Dependency injection, service lifecycle, and message-passing
+> framework for Go. Foundation layer for the Lethean ecosystem.
+
+## Entry Points
+
+- CLAUDE.md — Agent instructions, build commands, architecture overview
+- docs/RFC.md — API contract specification (start here for the full spec)
+
+## Package Layout
+
+- pkg/core/ — The Core struct: DI container, service registry, lifecycle, IPC
+- No subpackages — everything is in the root core package
+
+## Key Types
+
+- Core — Central application container (created via core.New())
+- Option — Single key-value pair {Key: string, Value: any}
+- Options — Collection of Option with typed accessors
+- Result — Universal return type {Value: any, OK: bool}
+- Service — Managed component with lifecycle (Startable/Stoppable)
+- Message — IPC message interface for ACTION/QUERY/PERFORM
+
+## Service Pattern
+
+Services register via factory functions:
+
+    core.New(
+        core.WithService(mypackage.Register),
+    )
+
+    func Register(c *core.Core) core.Result {
+        svc := &MyService{runtime: core.NewServiceRuntime(c, opts)}
+        return core.Result{Value: svc, OK: true}
+    }
+
+## Conventions
+
+Follows RFC-025 Agent Experience (AX) principles.
+See: https://core.help/specs/RFC-025-AGENT-EXPERIENCE/