Share vc-git from a single copy at the repository root

Four templates need it and two did not have it. The paper copy called
gawk -f ~/bin/vc-git.awk while shipping vc-git.awk beside itself, so it
only worked for someone who had also installed the awk script by hand;
it now calls the copy it ships with.

Templates link to ../../resources/, which new_tex_document has to
dereference when it extracts one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

letter_template/Makefile

@@ -14,7 +14,7 @@ viewpdf: all
 	evince *.pdf
 
 vc:
-	vc-git
+	resources/vc-git
 
 pdf: all
 

letter_template/resources/vc-git

@@ -0,0 +1 @@
+../../resources/vc-git

letter_template/resources/vc-git.awk

@@ -0,0 +1 @@
+../../resources/vc-git.awk