Add codespell support with configuration and fixes (#21807)

Co-authored-by: Claude Code 2.1.142 / Claude Opus 4.7 <noreply@anthropic.com>

.dockerignore

@@ -1,6 +1,6 @@
 # Actual layer caching is impossible due to .git, but
 # that must be included for provenance reasons.  These ignores
-# are strictly for hygenic build.
+# are strictly for hygienic build.
 *
 !/*.go
 !/go.*