fix: make solve-issue's docker-mode dep-install check unskippable

Fixed

• solve-issue's dependency step let a worker's own probing (checking for node_modules/.venv,
  a package manager on PATH, etc.) substitute for the docker-mode check, so a docker-mode
  project could skip straight to Step 3 without ever installing deps. The skill now tells the
  worker to run the docker-mode check first, before any other exploration, and makes explicit that
  docker mode's dep-install invocation is never optional or deferred to "if a command fails" —
  docker mode has no host-side fallback.
  • registry.json: solve-issue 1.9.9 -> 1.9.10 (skills/solve-issue/SKILL.md).