refactor: delete sync.sh, dev workflow moves to npx skills add . -g -y + native installers

Every job sync.sh did has a better replacement:

- Per-harness skill dirs (~/.claude/skills, ~/.codex/skills, ~/.agents/skills):
  `npx skills add . -g -y` writes to every detected harness's home dir and
  uses symlinks by default. Edits propagate live — no re-deploy step.
- Hermes (~/.hermes/skills/research/last30days):
  `hermes skills install mvanhorn/last30days-skill --force` pulls from
  GitHub and handles the deploy itself. The script wrapping was redundant.
- OpenClaw variant: `clawhub install last30days-official` is what users
  already run per the README; the maintainer doesn't need a separate
  variant-deploy step in the public repo's scripts.
- Claude marketplace cache (~/.claude/plugins/cache/...): this was a
  "test against the official install path" hack we shouldn't have been
  recommending. With PR #400's resolver collapse, STEP 0 no longer
  enforces the cache as the only valid SKILL.md location. Just install
  the skill normally via `npx skills` or the marketplace.

Cleanup:

- DELETE skills/last30days/scripts/sync.sh
- tests/test_version_consistency.py — drop test_sync_cache_path_uses_skill_version
- CLAUDE.md — replace the sync.sh command + rule with `npx skills add . -g -y`
- HERMES_SETUP.md — Installation now uses `hermes skills install --force`;
  developer-alternative section shows the symlink pattern for live editing
- render.py — _skill_version docstring no longer attributes the
  ".claude-plugin absent" case to sync.sh; explains it via per-harness
  install paths in general
- .github/PULL_REQUEST_TEMPLATE.md — drop the "Ran bash scripts/sync.sh"
  checklist item

CHANGELOG and historical docs (release notes, plan files) keep their
existing sync.sh mentions as accurate history.

tests/test_version_consistency.py

@@ -21,14 +21,6 @@ class TestVersionConsistency(unittest.TestCase):
         version = _skill_version()
         self.assertIn(f"# last30days v{version}:", text)
 
-    def test_sync_cache_path_uses_skill_version(self) -> None:
-        sync_text = (SKILL_ROOT / "scripts" / "sync.sh").read_text(encoding="utf-8")
-        version = _skill_version()
-        self.assertIn(
-            f'last30days-skill/last30days/{version}"',
-            sync_text,
-        )
-
     def test_memory_save_dir_uses_single_env_variable(self) -> None:
         skill_text = (SKILL_ROOT / "SKILL.md").read_text(encoding="utf-8")
         compare_text = (SKILL_ROOT / "scripts" / "compare.sh").read_text(encoding="utf-8")