refactor: inline all _speakeasy composite action calls into direct CLI calls

Replace every `uses: ./_speakeasy` with direct `run: speakeasy ci <action>`
shell steps across all internal workflow files. Each job now installs the
CLI directly and passes INPUT_* env vars explicitly, eliminating the need
for _speakeasy checkout steps.

This removes the dependency on pinned SHA checkouts of sdk-generation-action,
fixes the bug where git operations during generation wipe the _speakeasy
directory, and decouples workflows from the composite action wrapper.

Files changed:
- workflow-executor.yaml: inline generate + publish-event/log-result across 7 jobs
- sdk-publish.yaml: inline release + publish-event/log-result across 9 jobs
- sdk-test.yaml: inline test
- tag.yaml: inline tag
- action.yml: fix working-directory from /repo/ path

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: danielkov