Add ~/.omp config; nvim git-repo external; ya pkg install hook

- dot_omp: agent config/keybindings/mcp/themes/commands + loop defs,
  goals, run-loop.sh; dotstate config.yml symlink materialized; dbs,
  logs, sessions, memories, blobs, caches, .env (secret), and
  managed-skills excluded
- .chezmoiexternal.toml: prdlk/nvim as git-repo external — no
  refreshPeriod + ff-only pull, local checkout wins over remote
- yazi plugins: vendored source copies dropped (target-ignored already);
  package.toml is the manifest, installed via run_onchange ya pkg
  install hook; stale piper/easyjump pins bumped to match live content
- herdr: plugins/github checkout, logs, session.json, .bak,
  release-notes dropped from sync (herdr-managed machine state)

.chezmoiexternal.toml

@@ -0,0 +1,10 @@
+# External content — cloned/downloaded by chezmoi, not stored in this repo.
+
+# Neovim config lives in its own repo. No refreshPeriod: chezmoi clones it
+# when ~/.config/nvim is missing (fresh machine) and otherwise never pulls,
+# so the local checkout always wins over the remote.
+[".config/nvim"]
+    type = "git-repo"
+    url = "https://github.com/prdlk/nvim.git"
+    [".config/nvim".pull]
+        args = ["--ff-only"]