refactor(tools): bin/{subject}/{method} layout; Go serve+watch modules

Move serve/ (module) -> bin/server, tools/ -> bin/tools, replace bin/kb-watch
bash with bin/watch Go package; self-executing Go shebangs bin/serve.go and
bin/kb/watch.go; Docker + CI + git/import + docs repointed. Multi-stage image
builds static serve+watch binaries (no Go runtime in container).

bin/kb/watch.go

@@ -0,0 +1,23 @@
+//usr/bin/env go run "$0" "$@"; exit
+// bin/kb/watch.go - re-index the 2dph brain when corpus files change.
+//
+// Usage:
+//
+//	./bin/kb/watch.go [dir...]            # dirs default /corpus
+//	KB_WATCH_INTERVAL=15 ./bin/kb/watch.go
+//
+// Shebang trick: first line is a Go `//` comment; the real code lives in the
+// importable package (module path, never a relative import).
+// NOTE: never run `gofmt -w` on this file - it rewrites `//usr/bin/env` to
+// `// usr/...` and breaks the shebang.
+package main
+
+import (
+	"os"
+
+	"github.com/eSlider/2dph/bin/watch"
+)
+
+func main() {
+	watch.Run(os.Args[1:])
+}