chore: add README, Makefile, CI, lint config and --version

The repo had no README, Makefile, CI, linter config or version string.

- README.md: requirements (ffmpeg/ffprobe, plus yt-dlp for SoundCloud), build,
  the per-source credentials table, usage, the quality scale and the download
  database's migration behaviour. Every claim was checked against the code
  rather than written from memory, which is how the quality-range bug below was
  found. It also records the two deferred refactors (no shared HTTP layer, and
  metadata as map[string]any) so they are documented rather than lore, and
  notes that there is no LICENSE file.
- Makefile: build, install, test, race, cover, fmt, fmt-check, vet, lint,
  check, clean, help. `make build` stamps version/commit/date via -ldflags.
- .github/workflows/ci.yml: gofmt, vet, build, test and test -race, plus a
  lint job. The linter is intentionally unpinned, with a comment: a
  golangci-lint built against an older Go cannot analyse a go1.25 module, which
  is the same reason a locally installed staticcheck built with go1.24 cannot
  run here.
- .golangci.yml: standard set plus bodyclose, errorlint, nilerr and
  govet/copylocks. copylocks matters now that config.Config carries a mutex;
  bodyclose and errorlint target defects this codebase actually has.
- `rip --version` / `-V`, documented in the help output, falling back to the
  VCS revision the toolchain embeds for `go install` builds.

Fixes a bug introduced in the previous commit: Validate capped deezer quality
at 2 and soundcloud at 1, but config.toml.example documents deezer as 2/3/4 and
the global -q flag accepts 0-4, so a documented config would have failed to
load. deezer's buildFormatPriority treats anything >= 2 as FLAC and soundcloud
ignores the value entirely, so the real ceiling is 4 everywhere; only the Qobuz
and Beatport floor of 1 is a genuine constraint. Pinned with a test that walks
the whole documented range.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/config/config_test.go

@@ -154,7 +154,6 @@ func TestValidateRejectsBadValues(t *testing.T) {
 		{"qobuz quality 5", func(d *ConfigData) { d.Qobuz.Quality = 5 }, "qobuz.quality"},
 		{"beatport quality 0", func(d *ConfigData) { d.Beatport.Quality = 0 }, "beatport.quality"},
 		{"tidal quality 5", func(d *ConfigData) { d.Tidal.Quality = 5 }, "tidal.quality"},
-		{"deezer quality 3", func(d *ConfigData) { d.Deezer.Quality = 3 }, "deezer.quality"},
 		{"negative quality", func(d *ConfigData) { d.Tidal.Quality = -1 }, "tidal.quality"},
 		{"max_connections 0", func(d *ConfigData) { d.Downloads.MaxConnections = 0 }, "max_connections"},
 		{"max_connections negative", func(d *ConfigData) { d.Downloads.MaxConnections = -5 }, "max_connections"},
@@ -182,13 +181,40 @@ func TestValidateRejectsBadValues(t *testing.T) {
 	}
 }
 
+// TestValidateAcceptsDocumentedQualityValues pins the ranges documented in
+// config.toml.example. An earlier draft capped deezer at 2 and soundcloud at 1,
+// which would have made a config the example itself documents fail to load.
+func TestValidateAcceptsDocumentedQualityValues(t *testing.T) {
+	for q := 0; q <= 4; q++ {
+		d := DefaultConfigData()
+		applyRuntimeDefaults(&d)
+		d.Deezer.Quality = q
+		d.Soundcloud.Quality = q
+		d.Tidal.Quality = q
+		d.Yandex.Quality = q
+		if err := Validate(&d); err != nil {
+			t.Errorf("quality %d rejected: %v", q, err)
+		}
+	}
+	// Qobuz and Beatport have no tier 0.
+	for q := 1; q <= 4; q++ {
+		d := DefaultConfigData()
+		applyRuntimeDefaults(&d)
+		d.Qobuz.Quality = q
+		d.Beatport.Quality = q
+		if err := Validate(&d); err != nil {
+			t.Errorf("qobuz/beatport quality %d rejected: %v", q, err)
+		}
+	}
+}
+
 func TestValidateAcceptsValidValues(t *testing.T) {
 	d := DefaultConfigData()
 	applyRuntimeDefaults(&d)
 	// Negative requests_per_minute disables throttling, which is legitimate.
 	d.Downloads.RequestsPerMinute = -1
 	d.Soundcloud.Quality = 1
-	d.Deezer.Quality = 2
+	d.Deezer.Quality = 4
 	d.Qobuz.Quality = 4
 	if err := Validate(&d); err != nil {
 		t.Fatalf("Validate() = %v, want nil", err)