fix: document exported API, fix naming, and harden Downloadv1.3.3

The remaining golangci-lint findings. These land together because the
Url -> URL rename spans util.go, parsers.go and wrapper.go, and splitting
it would leave an intermediate commit that does not compile.

Download() carried the most serious bug here: try() only prints an error,
it does not return, so a failed request fell through to
resp.Body.Close() on a nil resp and panicked. Every failure path now
returns the zero Downloaded, and callers check Status. ReturnHTTPError
guards against the resulting status 0, which would otherwise panic
WriteHeader. Requests carry a context with a timeout (noctx), and a
download-proxy now routes through ProxiedTransport so it keeps the DA
throttle and timeouts.

Also:
- doc comments on all 48 exported symbols (revive's exported rule, with
  checkPrivateReceivers, since most of app is exported methods on the
  unexported skunkyart type), plus package docs in new doc.go files so
  both the embed and non-embed builds are covered.
- ST1003 naming: UrlBuilder -> URLBuilder, id_search -> idSearch,
  cache_config -> cacheConfig, TXT_RAW -> TxtRaw, mediaUrl -> mediaURL.
- explicit json tags on structs that are unmarshaled (musttag); the
  hyphenated keys already had tags, the rest relied on case-insensitive
  fallback. Behaviour is unchanged.
- modernization: range-over-int, WaitGroup.Go, stale +build lines,
  interface{} -> any, strings.Builder over string concatenation in a loop.

1 files changed, 7 insertions, 1 deletions

diff --git a/static/templates.go b/static/templates.go
index 28a057a..859f075 100755
--- a/static/templates.go
+++ b/static/templates.go
@@ -1,16 +1,22 @@
 //go:build embed
-// +build embed
 
 package static
 
 import "embed"
 
+// Templates is the asset filesystem compiled into the binary.
+//
 //go:embed *
 var Templates embed.FS
+
+// Enabled reports that assets are embedded in this build.
 var Enabled bool = true
 
+// StaticPath is accepted for parity with the non-embed build, where it names the
+// directory assets are read from. It is ignored here.
 var StaticPath string
 
+// CopyTemplatesToMemory is a no-op in this build: the assets are already embedded.
 func CopyTemplatesToMemory() {
 	_ = StaticPath
 }