fix(CI): resolve shellcheck and broken-symlink lint failures

The lint workflow added in #120 surfaced three pre-existing failures. This
commit fixes the two shellcheck findings and the broken symlink.

- init-guidance.sh: the first sed expression matches the literal text
  "${CLAUDE_PLUGIN_ROOT}" as it appears in the vendored SKILL.md, so the
  single quotes are required and SC2016 is a false positive. Disable the
  check at that call with a comment explaining why.

- upload-screenshots.sh: verify_on's retry loop never reads its counter, so
  SC2034 fired on it. Use the conventional throwaway `_` instead.

- .claude/rules/plugin-entity-taxonomy.md: the symlink still pointed at
  docs/guidance/, which ad6ee13 moved to
  han-plugin-builder/skills/guidance/references/. That commit rewrote the
  adjacent .claude/rules/ text references but could not catch a symlink
  target. Repoint it at the file's current home.

Author: mxriverlynn

.claude/rules/plugin-entity-taxonomy.md

@@ -1 +1 @@
-../../docs/guidance/plugin-entity-taxonomy.md
+../../han-plugin-builder/skills/guidance/references/plugin-entity-taxonomy.md

han-github/skills/work-items-to-issues/scripts/upload-screenshots.sh

@@ -132,8 +132,7 @@ put_file() {
 # authenticated viewers, so the issue body is correct.
 verify_on() {
   local branch="$1" api_path="$2"
-  local attempt
-  for attempt in 1 2 3 4 5; do
+  for _ in 1 2 3 4 5; do
     if gh api "$api_path?ref=$branch" --jq .sha >/dev/null 2>&1; then
       return 0
     fi

han-plugin-builder/skills/guidance/scripts/init-guidance.sh

@@ -51,6 +51,10 @@ RULE=".claude/rules/plugin-building-guidance.md"
 rewrite_skill() {
   file="$1"
   tmp="$(mktemp)"
+  # SC2016 is disabled deliberately: the first expression matches the literal
+  # text "${CLAUDE_PLUGIN_ROOT}" as it appears in the vendored SKILL.md, so the
+  # single quotes are required. Expanding it here would match nothing.
+  # shellcheck disable=SC2016
   sed \
     -e 's|${CLAUDE_PLUGIN_ROOT}/skills/guidance/references/|.claude/skills/plugin-guidance/references/|g' \
     -e 's|^name: guidance$|name: plugin-guidance|' \