fix(skill): use find instead of ls+glob in cache resolvers (zsh compatibility)

zsh errors on globs that match nothing instead of returning the literal
pattern (bash's default), and `2>/dev/null` does not suppress the error
because it comes from the shell's glob expansion before `ls` even runs.
Under Codex (which executes the SKILL.md bash via zsh), STEP 0 and the
Step 1 / comparison-mode resolvers emitted noisy "no matches found"
errors on machines without a Claude plugin cache populated.

Replaces all three `ls -d $HOME/.claude/plugins/cache/last30days-skill/last30days/*/`
invocations with `find ... -mindepth 1 -maxdepth 1 -type d 2>/dev/null`.
find is POSIX-portable, errors silently when the base dir doesn't exist,
and never triggers shell glob errors. `sort -V | tail -1` precedence
preserved (verified: picks 3.10.0 over 3.2.1 over 3.1.0). Trailing-slash
strip removed because find doesn't append slashes.

Observed in Codex session running /last30days against PR #400 with the
Claude plugin cache deleted - bash output was:
  zsh:1: no matches found: /Users/.../last30days/*/

After fix: clean empty output, exit 0, STEP 0 correctly treats it as
"no cache present, do not hop", resolver falls through to per-harness
skill dirs as designed.

skills/last30days/SKILL.md

@@ -67,7 +67,7 @@ Before reading anything else in this file, check whether you loaded SKILL.md fro
 **Run this check:**
 
 ```bash
-CLAUDE_CACHE_LATEST=$(ls -d "$HOME/.claude/plugins/cache/last30days-skill/last30days"/*/ 2>/dev/null | sort -V | tail -1)
+CLAUDE_CACHE_LATEST=$(find "$HOME/.claude/plugins/cache/last30days-skill/last30days" -mindepth 1 -maxdepth 1 -type d 2>/dev/null | sort -V | tail -1)
 CLAUDE_CACHE_LATEST="${CLAUDE_CACHE_LATEST%/}"
 echo "CLAUDE_CACHE_LATEST=$CLAUDE_CACHE_LATEST"
 ```
@@ -586,8 +586,7 @@ When the user asks "X vs Y" (or "X vs Y vs Z"), the engine fans out N full `pipe
 # Comparison mode skips Step 1, so resolve SKILL_ROOT inline here (same precedence
 # walk as Step 1 — keep the two in sync if you edit either).
 SKILL_ROOT=""
-CLAUDE_PLUGIN_ROOT="$(ls -d "$HOME/.claude/plugins/cache/last30days-skill/last30days/"*/ 2>/dev/null | sort -V | tail -1)"
+CLAUDE_PLUGIN_ROOT="$(find "$HOME/.claude/plugins/cache/last30days-skill/last30days" -mindepth 1 -maxdepth 1 -type d 2>/dev/null | sort -V | tail -1)"
-CLAUDE_PLUGIN_ROOT="${CLAUDE_PLUGIN_ROOT%/}"
 if [ -n "$CLAUDE_PLUGIN_ROOT" ]; then
   if [ -f "$CLAUDE_PLUGIN_ROOT/skills/last30days/scripts/last30days.py" ]; then
     SKILL_ROOT="$CLAUDE_PLUGIN_ROOT/skills/last30days"
@@ -900,8 +899,9 @@ SKILL_ROOT=""
 
 # 1. Claude Code plugin cache (versioned, sort -V picks freshest). Two cache layouts ship in the wild:
 #    nested ({cache}/{version}/skills/last30days/scripts/...) and flat ({cache}/{version}/scripts/...).
-CLAUDE_PLUGIN_ROOT="$(ls -d "$HOME/.claude/plugins/cache/last30days-skill/last30days/"*/ 2>/dev/null | sort -V | tail -1)"
+# `find` (not `ls + glob`) because zsh errors on globs that match nothing, leaking
-CLAUDE_PLUGIN_ROOT="${CLAUDE_PLUGIN_ROOT%/}"
+# noisy "no matches found" stderr in Codex/zsh sessions even with 2>/dev/null.
+CLAUDE_PLUGIN_ROOT="$(find "$HOME/.claude/plugins/cache/last30days-skill/last30days" -mindepth 1 -maxdepth 1 -type d 2>/dev/null | sort -V | tail -1)"
 if [ -n "$CLAUDE_PLUGIN_ROOT" ]; then
   if [ -f "$CLAUDE_PLUGIN_ROOT/skills/last30days/scripts/last30days.py" ]; then
     SKILL_ROOT="$CLAUDE_PLUGIN_ROOT/skills/last30days"