Add tracing manifests and docs; clean up branch lint findings

Manager env block (downward-API resource attrs, commented OTLP
examples), architecture §10 + Decisions entries, README section.
Lint: goconst constants, gofmt, logcheck (Setup now takes its logger
from ctx via logf.FromContext).

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

internal/tracing/logger.go

@@ -47,6 +47,8 @@ func StartSpan(ctx context.Context, tracer trace.Tracer, name string, opts ...tr
 // base for span enrichment. If ctx already carries a valid span (the HTTP
 // middleware calls this inside the otelhttp handler), the logger is
 // enriched immediately.
+//
+//nolint:logcheck // IntoContext-analogue: taking ctx and the logger to seed it with is the point.
 func ContextWithLogger(ctx context.Context, base logr.Logger) context.Context {
 	ctx = context.WithValue(ctx, baseLoggerKey{}, base)
 	if sc := trace.SpanContextFromContext(ctx); sc.IsValid() {