chore(claude): add hooks, skills, and agents for Claude Code (#496)

* chore(claude): add hooks, skills, and agents for Claude Code

Add auto-formatting hooks (ruff, shfmt, prettier, actionlint),
rules.yml edit blocker, 5 skills (/release, /test-action,
/new-action, /validate, /check-pins), and 2 subagents
(action-validator, test-coverage-reviewer). Update CLAUDE.md
with hook documentation.

* fix(claude): add tool availability guards and fix skill docs

Add jq availability checks to hook scripts (block-rules-yml.sh,
post-edit-write.sh) and wrap actionlint call in command -v guard,
consistent with project rules #2 and #10. Fix validate skill to
reflect actual make all pipeline order and note that make test
runs separately.

* fix(claude): correct skill docs per PR review feedback

Fix validate skill description to say "precommit" instead of "test",
and fix check-pins SHA guidance to use origin/main instead of HEAD.

* feat(tools): add SHA-pinning enforcement to check-version-refs

The check-version-refs script previously only displayed existing
SHA-pinned refs but silently skipped non-SHA references. Add a
validation pass that detects and reports any ivuorinen/actions/*
references not using a 40-char hex SHA, exiting 1 on violations.

* fix(tools): fix temp file leak in check-version-refs.sh

Write find output directly to $violations_file instead of
$violations_file.all so the EXIT trap covers cleanup on all
exit paths, not just the happy path.

.claude/settings.json

@@ -0,0 +1,26 @@
+{
+  "hooks": {
+    "PreToolUse": [
+      {
+        "matcher": "Edit|Write",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "\"$CLAUDE_PROJECT_DIR\"/.claude/hooks/block-rules-yml.sh"
+          }
+        ]
+      }
+    ],
+    "PostToolUse": [
+      {
+        "matcher": "Edit|Write",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "\"$CLAUDE_PROJECT_DIR\"/.claude/hooks/post-edit-write.sh"
+          }
+        ]
+      }
+    ]
+  }
+}