Run wrapped tools directly as vintner <tool> ..., no PATH needed

`vintner cl ...`, `vintner msbuild ...`, etc. now work without adding
<dest>/bin/<arch> to PATH or relying on the same-directory symlinks
`install` sets up there. wrapper.Run gained an explicit binDir
parameter (empty string preserves the existing os.Executable()-based
self-location for the ordinary multi-call/symlink case) so
cmd/vintner's new runTool can point it at a resolved toolchain
directory instead.

Resolution order: VINTNER_BIN if set (same meaning as `env --bin` -
point it at a <dest>/bin/<arch> directory directly, for a non-default
--dest or a specific architecture), else <defaultToolchainDir>/bin/
<hostArch> - the layout a plain `vintner download && vintner install`
with no --dest override produces. A missing toolchain gets a clear
error pointing at both fixes, rather than bubbling up whatever
wineenv.Load's env.json error looks like.

Also fixed shell completion falling out of sync with the actual tool
list: the bash/zsh scripts previously hand-copied tool/flag names
(and had already gone stale once - --with-dxsdk was missing from the
download flag completions since it was added). The tool name list is
now generated from wrapper.ToolNames() instead of hand-maintained,
and both scripts now complete tool names too, so `vintner <TAB>`
suggests `cl`, `link`, `msbuild`, etc. alongside the management
subcommands.

Verified end-to-end with a minimal PATH (/usr/bin:/bin only, no
toolchain dir on it at all): `vintner cl /nologo hello.c` compiled
successfully, and `vintner msbuild -t:Rebuild ...` rebuilt the same
real KMDF driver verified earlier this session - both via the default
~/.vintner/bin/<hostArch> resolution, no VINTNER_BIN override needed.

internal/wrapper/tools.go

@@ -4,7 +4,11 @@
 // filtering its output.
 package wrapper
 
-import "github.com/Cheviiot/vintner/internal/wineenv"
+import (
+	"sort"
+
+	"github.com/Cheviiot/vintner/internal/wineenv"
+)
 
 // dirKind selects which install directory a tool's real .exe lives in.
 type dirKind int
@@ -46,6 +50,32 @@ var Tools = map[string]spec{
 // nativeTools are handled entirely without Wine.
 var nativeTools = map[string]bool{"cmd": true, "findstr": true}
 
+// IsTool reports whether name is a recognized wrapped tool - either a
+// Wine-hosted one in Tools or a native shim in nativeTools. Shared between
+// the ordinary multi-call dispatch (invoked *as* one of these names via a
+// same-directory symlink) and `vintner <tool> ...` direct dispatch, so both
+// recognize exactly the same set of names.
+func IsTool(name string) bool {
+	_, ok := Tools[name]
+	return ok || nativeTools[name]
+}
+
+// ToolNames returns every recognized tool name, sorted - Tools and
+// nativeTools combined. Used to generate shell completion without a
+// separate hand-maintained list that could drift from the real set (as
+// happened once already with a stale --with-dxsdk completion entry).
+func ToolNames() []string {
+	names := make([]string, 0, len(Tools)+len(nativeTools))
+	for name := range Tools {
+		names = append(names, name)
+	}
+	for name := range nativeTools {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	return names
+}
+
 func (s spec) exeDir(p *wineenv.Paths) string {
 	switch s.dir {
 	case dirSDK: