feat(modules): embed built-in modules in the binary (#316)

modules loaded only from an exe-adjacent modules/ dir or ~/.config, so a
bare `go install`ed binary shipped zero modules. embed the modules/ tree
and fall back to it when no filesystem builtin dir is found.

the on-disk builtin dir and the user-override dir still take precedence,
so a dev tree and a release that ships the folder alongside the binary
keep working unchanged. the embed directive lives at the repo root
because go:embed cannot reach a parent directory, and it registers the
filesystem with the loader through a package hook to avoid an import
cycle back into the root package.

embed_modules.go

@@ -0,0 +1,40 @@
+/*
+·━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━·
+:                                                                               :
+:   █▀ █ █▀▀   ·   Blazing-fast pentesting suite                                :
+:   ▄█ █ █▀    ·   BSD 3-Clause License                                         :
+:                                                                               :
+:   (c) 2022-2026 vmfunc, xyzeva,                                               :
+:                 lunchcat alumni & contributors                                :
+:                                                                               :
+·━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━·
+*/
+
+package sif
+
+import (
+	"embed"
+	"io/fs"
+
+	"github.com/charmbracelet/log"
+	"github.com/vmfunc/sif/internal/modules"
+)
+
+// builtinModules embeds the module tree into the binary. this file lives at the
+// repo root because go:embed cannot reference a parent directory, and modules/
+// sits above internal/modules where the loader lives.
+//
+//go:embed modules
+var builtinModules embed.FS
+
+// register the embedded modules with the loader once, rooted at the modules
+// directory so paths match the on-disk layout. the loader only uses this as a
+// fallback when no filesystem modules/ dir is present.
+func init() {
+	sub, err := fs.Sub(builtinModules, "modules")
+	if err != nil {
+		log.Debugf("embedded modules unavailable: %v", err)
+		return
+	}
+	modules.SetBuiltinFS(sub)
+}