Add paid-media category to scripts and CI workflow

Prepares infrastructure for the upcoming Paid Media Division (PR #83).
Registers paid-media in convert.sh, lint-agents.sh, install.sh, and
the lint-agents GitHub Actions workflow.

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

scripts/install.sh

@@ -259,7 +259,7 @@ install_claude_code() {
   local count=0
   mkdir -p "$dest"
   local dir f first_line
-  for dir in design engineering marketing product project-management \
+  for dir in design engineering marketing paid-media product project-management \
               testing support spatial-computing specialized; do
     [[ -d "$REPO_ROOT/$dir" ]] || continue
     while IFS= read -r -d '' f; do