provision: install herdr

[samialdury]

Adds a herdr provisioning module, following the existing style.

• provision/herdr.sh — user-level install into ~/.local/bin via curl -fsSL https://herdr.dev/install.sh | sh, so no require_sudo. Two-branch skip (has_cmd herdr or -x ~/.local/bin/herdr), because a fresh install is not on the calling shell's PATH yet — same reason as claude.sh. Ends with show_versions herdr, resolved through PATH.
• No signature/checksum verification: herdr publishes no signed release manifest, so there is nothing to pin against.
• run-all.sh — herdr after claude; both are user-level ~/.local/bin installers.
• test/inside.sh — herdr in both idempotency rounds, plus assertions for the skip path and a readable version.
• Config linking is unchanged: .config/herdr/config.toml already links via LINKS_ZSH.

Verification

./scripts/test-install.sh and ./provision/test/run.sh both pass:

  !! herdr already installed at /home/dev/.local/bin/herdr; skipping install
  ok herdr: herdr 0.7.5 (/home/dev/.local/bin/herdr)
ok all container checks passed

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