fix(codegen): Skip empty descriptions instead of emitting empty doc comments

`app.bsky.ageassurance.defs` carries `"description": ""`, which generated a
bare `///` and tripped `clippy::empty_docs`. Since CI runs with
`RUSTFLAGS: "-D warnings"`, that alone fails the build on regeneration.

Treat an empty description the same as a missing one, both for the
per-item `#[doc]` and the schema-level `#![doc]`.

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

Author: sugyan

lexicon/atrium-codegen/src/generator.rs

@@ -62,7 +62,9 @@ pub(crate) fn generate_schemas(
 
         let documentation = {
             let doc = format!("Definitions for the `{}` namespace.", schema.id);
-            let description = if let Some(description) = &schema.description {
+            let description = if let Some(description) =
+                schema.description.as_deref().filter(|s| !s.is_empty())
+            {
                 quote!(#![doc = #description])
             } else {
                 quote!()

lexicon/atrium-codegen/src/token_stream.rs

@@ -585,7 +585,8 @@ fn unknown_type(unknown: &LexUnknown) -> Result<(TokenStream, TokenStream)> {
 }
 
 fn description(description: &Option<String>) -> TokenStream {
-    if let Some(description) = description {
+    // An empty description would emit an empty doc comment, which trips `clippy::empty_docs`.
+    if let Some(description) = description.as_deref().filter(|s| !s.is_empty()) {
         quote!(#[doc = #description])
     } else {
         quote!()