feat: builder + App runner, Makefile (v1.1.0)

Builder (cli.For[C]): Root/Dir/Cmd/SlotDir/Slot construct the tree
without repeating the [C] type parameter at every node; returns plain
*Node[C] so it interoperates with struct-literal construction.

App[C]: collapses the per-binary main.go — standard flags
(-color/-json/-version, -server when configured), mode-aware color
defaults, version banner, client connect, and the one-shot-vs-shell
split — into one Main(). Transport-agnostic via a Connect callback, so
it never assumes gRPC.

Makefile: `make check` = fixstyle vet lint test (the pre-commit gate),
plus build and a linux+openbsd cross target. The example now dogfoods
both Builder and App. Tests cover the builder tree and App's one-shot
dispatch / -version / nil-Connect paths.

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

docs/PROPOSAL.md

@@ -105,15 +105,18 @@ Module: `git.ipng.ch/ipng/golang-cli` (matches your git host). Single package
   go.sum
   LICENSE                      Apache-2.0 (matches the SPDX headers already in the files)
   README.md
+  Makefile       check (= fixstyle vet lint test), build, cross (linux + openbsd)
   tree.go        Node[C], Walk, matchFixedChild, findSlotChild, expandPaths, Candidates
   tree_test.go   table tests over a fixture tree (no client needed; Walk ignores Dynamic)
+  builder.go     For[C] / Builder[C]: Root/Dir/Cmd/SlotDir/Slot (no repeated [C])
   complete.go    completer[C], questionListener[C], SplitTokens, splitForCompletion
   shell.go       Shell[C] (config + Run), Dispatch, showHelpAt, unknownCommandError, ErrQuit
+  app.go         App[C]: standard flags + banner + connect + one-shot/shell -> Main()
   color.go       SetColor, Paint, Label + the ANSI palette (Red/Green/Blue/Yellow/Cyan)
   output.go      SetFormat, Emit (text-or-JSON), KV, IsJSON
   term_openbsd.go   applyTermFuncs (//go:build openbsd)         <- from shell_term_openbsd.go
   term_default.go   applyTermFuncs no-op (//go:build !openbsd)  <- from shell_term_default.go
-  example/main.go   self-contained, dependency-free demo CLI
+  example/main.go   self-contained, dependency-free demo CLI (uses Builder + App)
   keypress/         (optional) WaitForKeypress + cbreak shim, per-GOOS  <- §4.3
 ```