fix(cli): stop reads only composeProjectName so a broken config can still stop the stack

[nicosampler]

Summary

Closes #25

stop validated the full config before shelling out to Docker Compose, so any
config error left a running stack that the tool could not bring down. Tearing
the stack down only needs the Compose project name, so stop now reads just
that field.

Changes

• stop is dispatched before loadConfig() and tears the stack down with
  docker compose --project-name <name> down --remove-orphans, which finds the
  containers by project label without compose files, env files, or profiles.
• New parseComposeProjectName (pure) and loadComposeProjectName in
  src/config.js: only composeProjectName is validated; everything else,
  including the version gate, is ignored.
• New stopStackByProjectName in src/compose.js; the docker spawn logic is
  extracted into a shared runDocker helper reused by runDockerCompose.
• README: stop removed from the config-reading commands in the lifecycle
  diagram, plus a note under CLI reference explaining the behavior.
• Changeset (patch).

Acceptance criteria

Suggested from the issue's expected behavior (it has no formal AC list):

• stop stops the stack when the config is broken but composeProjectName is a valid non-empty string
• stop fails with the usual config error when composeProjectName is missing or invalid
• Every other Docker command keeps validating the full config

Test plan

Automated tests

scripts/config-validation.test.js: 4 new cases for parseComposeProjectName
(valid config, config that full validation rejects, missing field, empty field).
Run with npm test (30 passing).

Manual verification

1. With "version": 0 plus an unknown field and a valid composeProjectName,
   stop runs the compose down and exits 0.
2. With composeProjectName empty or missing, stop prints the config error
   and exits 1.

Breaking changes

None.

Checklist

• Self-reviewed my own diff
• Tests added or updated
• Docs updated (if applicable)
• No unrelated changes bundled in

Screenshots

None.

[gemini-code-assist]

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