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.

skills/last30days/scripts/lib/render.py

@@ -21,9 +21,11 @@ _VERSION_RE = re.compile(
 def _skill_version() -> str:
     """Read plugin version from .claude-plugin/plugin.json, falling back to SKILL.md frontmatter.
 
-    sync.sh does not copy .claude-plugin/ to non-cache install dirs (~/.codex/skills,
-    ~/.agents/skills, Hermes), so SKILL.md frontmatter is the fallback that keeps the
-    badge from emitting v? on those installs. Returns "?" only if both sources are missing.
+    Per-harness skill install dirs (`~/.claude/skills`, `~/.codex/skills`, `~/.agents/skills`,
+    Hermes, etc.) do not always carry `.claude-plugin/plugin.json` — that file ships with
+    plugin-cache installs but not with per-harness skill installs. SKILL.md frontmatter is
+    the fallback that keeps the badge from emitting v? on those installs. Returns "?" only
+    if both sources are missing.
 
     A corrupt manifest at one ancestor does not shadow a valid manifest at a deeper one
     (continue, not break). YAML frontmatter accepts double-quoted, single-quoted, or