P0: stand up executus harness module above majordomo

Batteries-included agent-harness base, extracted from mort's agent layer.
This first cut establishes the module + the zero-coupling core primitives:

- lane, dispatchguard, pendingattach, run/progress.go: moved verbatim from mort
- config: host config Source seam + env-var default (nil-safe helpers)
- deliver: output-egress seam + Discard/Stdout defaults
- identity: AdminPolicy + MemberResolver seams (nil-safe)
- fanout: programmatic N×M swarm (bounded global + per-key concurrency)
- README/CLAUDE.md with the vibe-coded banner; CI with Go gates +
  the "core stays majordomo+stdlib only" invariant

Core builds with stdlib only today; majordomo enters at P1 (model/structured).
go build/vet/test -race all green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1,27 +1,20 @@
-# ---> Go
-# If you prefer the allow list template instead of the deny list, see community template:
-# https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
-#
-# Binaries for programs and plugins
+# Binaries
 *.exe
-*.exe~
-*.dll
-*.so
-*.dylib
-
-# Test binary, built with `go test -c`
 *.test
-
-# Output of the go coverage tool, specifically when used with LiteIDE
 *.out
+/bin/
+/dist/
 
-# Dependency directories (remove the comment below to include it)
-# vendor/
-
-# Go workspace file
+# Go workspace / local overrides
 go.work
 go.work.sum
 
-# env file
+# Env / secrets (never commit)
 .env
+.env.*
+!.env.example
 
+# Editor / OS
+.idea/
+.vscode/
+.DS_Store