fix: inline albers.js script tag via header-includes to fix vignette build

Replace `in_header: albers-header.html` with pandoc's top-level
`header-includes` field in all four vignettes. This avoids pandoc's
file lookup (error 99) during R CMD check by inlining the single-line
script tag directly in the YAML.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: bbuchsbaum

vignettes/confounds-and-variables.Rmd

@@ -5,15 +5,14 @@ output:
     toc: yes
     toc_depth: 2.0
     css: albers.css
-    includes:
-      in_header: albers-header.html
+header-includes:
+  - '<script src="albers.js"></script>'
 params:
   family: red
   preset: homage
 resource_files:
 - albers.css
 - albers.js
-- albers-header.html
 
 vignette: |
   %\VignetteIndexEntry{Working with Confounds and Variables}

vignettes/derivatives.Rmd

@@ -5,15 +5,14 @@ output:
     toc: yes
     toc_depth: 2.0
     css: albers.css
-    includes:
-      in_header: albers-header.html
+header-includes:
+  - '<script src="albers.js"></script>'
 params:
   family: red
   preset: homage
 resource_files:
 - albers.css
 - albers.js
-- albers-header.html
 
 vignette: |
   %\VignetteIndexEntry{Work With Derivatives and Confounds}

vignettes/mock-bids.Rmd

@@ -5,15 +5,14 @@ output:
     toc: yes
     toc_depth: 2.0
     css: albers.css
-    includes:
-      in_header: albers-header.html
+header-includes:
+  - '<script src="albers.js"></script>'
 params:
   family: red
   preset: homage
 resource_files:
 - albers.css
 - albers.js
-- albers-header.html
 
 vignette: |
   %\VignetteIndexEntry{Create Mock BIDS Projects for Tests and Examples}

vignettes/quickstart.Rmd

@@ -5,15 +5,14 @@ output:
     toc: yes
     toc_depth: 2.0
     css: albers.css
-    includes:
-      in_header: albers-header.html
+header-includes:
+  - '<script src="albers.js"></script>'
 params:
   family: red
   preset: homage
 resource_files:
 - albers.css
 - albers.js
-- albers-header.html
 
 vignette: |
   %\VignetteIndexEntry{Getting Started with bidser}