feat(ffmpeg): add ffmpegdist classifier for eugeneware/ffmpeg-static

Upstream uses non-standard OS/arch names (x64, ia32, win32, arm) and
ships both bare binaries and .gz-compressed copies. classifyFFmpegDist
maps those to canonical names and keeps only bare binaries.

Also adds source-override logic to installerconf so that
github_releases + source = ffmpegdist works: GitHub is used for
fetching while the custom classifier handles classification.

internal/classifypkg/classifypkg.go

@@ -166,6 +166,8 @@ func classifySource(pkg string, conf *installerconf.Conf, d *rawcache.Dir) ([]st
 		return classifyMariaDBDist(d)
 	case "zigdist":
 		return classifyZigDist(d)
+	case "ffmpegdist":
+		return classifyFFmpegDist(d)
 	default:
 		return nil, nil
 	}
@@ -464,6 +466,86 @@ func classifyGitHub(pkg string, conf *installerconf.Conf, d *rawcache.Dir) ([]st
 	return assets, nil
 }
 
+var ffmpegOSMap = map[string]string{
+	"linux":  "linux",
+	"darwin": "darwin",
+	"win32":  "windows",
+}
+
+var ffmpegArchMap = map[string]string{
+	"x64":   "x86_64",
+	"ia32":  "x86",
+	"arm64": "aarch64",
+	"arm":   "armv7",
+}
+
+// classifyFFmpegDist handles eugeneware/ffmpeg-static releases.
+// Upstream uses non-standard names (x64, ia32, win32, arm) and ships both
+// bare binaries and .gz-compressed copies. Only bare binaries are kept —
+// the install template has no handler for single-file .gz extraction.
+func classifyFFmpegDist(d *rawcache.Dir) ([]storage.Asset, error) {
+	releases, err := ReadAllRaw(d)
+	if err != nil {
+		return nil, err
+	}
+
+	var assets []storage.Asset
+	for _, data := range releases {
+		var rel ghRelease
+		if err := json.Unmarshal(data, &rel); err != nil {
+			continue
+		}
+		if rel.Draft {
+			continue
+		}
+
+		version := strings.TrimPrefix(rel.TagName, "b")
+
+		channel := "stable"
+		if rel.Prerelease {
+			channel = "beta"
+		}
+
+		date := ""
+		if len(rel.PublishedAt) >= 10 {
+			date = rel.PublishedAt[:10]
+		}
+
+		for _, a := range rel.Assets {
+			if strings.Contains(a.Name, ".") {
+				continue
+			}
+			if !strings.HasPrefix(a.Name, "ffmpeg-") {
+				continue
+			}
+
+			parts := strings.SplitN(a.Name, "-", 3)
+			if len(parts) != 3 {
+				continue
+			}
+
+			os, osOK := ffmpegOSMap[parts[1]]
+			arch, archOK := ffmpegArchMap[parts[2]]
+			if !osOK || !archOK {
+				continue
+			}
+
+			assets = append(assets, storage.Asset{
+				Filename: a.Name,
+				Version:  version,
+				Channel:  channel,
+				OS:       os,
+				Arch:     arch,
+				Format:   "",
+				Download: a.BrowserDownloadURL,
+				Date:     date,
+			})
+		}
+	}
+
+	return assets, nil
+}
+
 // classifyServiceman handles serviceman's dual-repo layout: binary releases
 // from therootcompany/serviceman (≤v0.8.x) and source-only releases from
 // bnnanet/serviceman (v0.9.x+). Emits binary assets where available, plus