fix: quote argument-hint values that YAML parses as arrays

Three command files declared argument-hint with an unquoted flow sequence, so a
strict YAML parse yields an array instead of a string. Harnesses that validate
the field reject the whole file: Qwen Code drops the command with
'frontmatter: Expected string, received array' and the slash command silently
disappears from the catalog.

Quote all three to match the convention already used by plan-canvas.md, pr.md,
prp-pr.md, plan-prd.md and the other argument-hint declarations in commands/.

commands/code-review.md

@@ -1,6 +1,6 @@
 ---
 description: Code review — local uncommitted changes or GitHub PR (pass PR number/URL for PR mode). Use for a step-by-step PRP-style checklist review; for a multi-agent pass use /review-pr, and for the adversarially-verified Workflow pass use /orch-review.
-argument-hint: [pr-number | pr-url | blank for local review]
+argument-hint: "[pr-number | pr-url | blank for local review]"
 ---
 
 # Code Review

commands/cost-report.md

@@ -1,6 +1,6 @@
 ---
 description: Generate a local Claude Code cost report from the ECC cost-tracker metrics log. Use for a terminal summary or CSV export of tracked spend; the cost-tracking skill covers the same metrics log for on-demand cost/budget questions asked in conversation.
-argument-hint: [csv]
+argument-hint: "[csv]"
 ---
 
 # Cost Report

commands/orch-review.md

@@ -1,6 +1,6 @@
 ---
 description: Run the orch-review native Workflow over a diff (local changes or a GitHub PR) and report blocking vs advisory findings. Surface for the orch-review workflow. Use for a native-Workflow, adversarially-verified multi-dimension review with fan-out and dedup; for the step-by-step checklist pass use /code-review, and for the multi-agent pass use /review-pr.
-argument-hint: [pr-number | pr-url | blank for local uncommitted changes]
+argument-hint: "[pr-number | pr-url | blank for local uncommitted changes]"
 ---
 
 # /orch-review