fix(classify): add package-specific overrides for sass, ffmpeg, go arm

- sass: bare arm → armv7 (Dart Sass targets ARMv7, not v6)
- ffmpeg: Windows .gz → ext exe (gzipped bare executables)
- go: keep bare arm as-is from Go dist API (matches production)

Reduces comparecache diffs from 6 packages to 3 (iterm2 channel edge
cases, postgres legacy ext, terraform alpha detection — all understood).

internal/classifypkg/classifypkg.go

@@ -22,6 +22,7 @@ import (
 	"github.com/webinstall/webi-installers/internal/rawcache"
 	"github.com/webinstall/webi-installers/internal/releases/bun"
 	"github.com/webinstall/webi-installers/internal/releases/chromedist"
+	"github.com/webinstall/webi-installers/internal/releases/ffmpeg"
 	"github.com/webinstall/webi-installers/internal/releases/fish"
 	"github.com/webinstall/webi-installers/internal/releases/gitea"
 	"github.com/webinstall/webi-installers/internal/releases/flutterdist"
@@ -37,6 +38,7 @@ import (
 	"github.com/webinstall/webi-installers/internal/releases/ollama"
 	"github.com/webinstall/webi-installers/internal/releases/pwsh"
 	"github.com/webinstall/webi-installers/internal/releases/postgres"
+	"github.com/webinstall/webi-installers/internal/releases/sass"
 	"github.com/webinstall/webi-installers/internal/releases/watchexec"
 	"github.com/webinstall/webi-installers/internal/releases/xcaddy"
 	"github.com/webinstall/webi-installers/internal/releases/zigdist"
@@ -149,6 +151,8 @@ func TagVariants(pkg string, assets []storage.Asset) {
 	switch pkg {
 	case "bun":
 		bun.TagVariants(assets)
+	case "ffmpeg":
+		ffmpeg.TagVariants(assets)
 	case "fish":
 		fish.TagVariants(assets)
 	case "git":
@@ -163,6 +167,8 @@ func TagVariants(pkg string, assets []storage.Asset) {
 		ollama.TagVariants(assets)
 	case "pwsh":
 		pwsh.TagVariants(assets)
+	case "sass":
+		sass.TagVariants(assets)
 	case "xcaddy":
 		xcaddy.TagVariants(assets)
 	}
@@ -877,7 +883,9 @@ func normalizeGoArch(goarch string) string {
 	case "386":
 		return "x86"
 	case "arm":
-		return "armv6"
+		// Go API uses bare "arm" — keep as-is to match production.
+		// The resolver handles arm compatibility (armv7→armv6 fallback).
+		return "arm"
 	case "ppc64le":
 		return "ppc64le"
 	case "ppc64":

internal/releases/ffmpeg/variants.go

@@ -0,0 +1,29 @@
+// Package ffmpeg provides variant tagging for ffmpeg-static releases.
+//
+// ffmpeg-static publishes bare executables for Windows. The .gz files
+// are gzip-compressed bare executables (not archives). Production
+// classifies these as ext "exe".
+package ffmpeg
+
+import (
+	"github.com/webinstall/webi-installers/internal/storage"
+)
+
+// TagVariants fixes Windows asset extensions for ffmpeg.
+//
+// Windows .gz files contain a gzipped bare executable, not a tar archive.
+// Production treats these as ext "exe". Bare Windows files (no extension)
+// are also executables.
+func TagVariants(assets []storage.Asset) {
+	for i := range assets {
+		if assets[i].OS != "windows" {
+			continue
+		}
+		switch assets[i].Format {
+		case ".gz":
+			assets[i].Format = ".exe"
+		case "":
+			assets[i].Format = ".exe"
+		}
+	}
+}

internal/releases/sass/variants.go

@@ -0,0 +1,19 @@
+// Package sass provides variant tagging for Dart Sass releases.
+//
+// Dart Sass uses bare "arm" in filenames to mean ARMv7 (the Dart VM's
+// minimum ARM target). The generic classifier maps bare "arm" to armv6,
+// so we correct it here.
+package sass
+
+import (
+	"github.com/webinstall/webi-installers/internal/storage"
+)
+
+// TagVariants remaps bare arm → armv7 for Dart Sass assets.
+func TagVariants(assets []storage.Asset) {
+	for i := range assets {
+		if assets[i].Arch == "armv6" {
+			assets[i].Arch = "armv7"
+		}
+	}
+}