Consolidate mw-dev test harness

[bill-ph]

Summary

• move the shared dev-backed harness under tests/mw-dev and keep the e2e payload under tests/mw-dev/e2e
• update e2e-mw-dev to use the shared harness commands
• simplify scenario-dev to isolated-only scenario.full using e2e-style mw-dev constants and generated per-run secrets
• remove obsolete tests/scenario-dev runner scripts and update docs/recipes

Verification

• go test -count=1 ./tests/scenario ./tests/mw-dev ./tests/manifests
• go test -count=1 ./tests/mw-dev/...
• bash -n tests/mw-dev/run.sh
• just lint
• just test-unit

[github-actions]

Test Impact Plan

Deterministic summary of how this PR changes tests, CI runners, and coverage-risk signals.

Summary

Area	Added	Changed	Deleted
Test files	0	58	2
E2E/journey files	0	0	5
Workflow files	0	2	0

Signals

• Test cases: +4 / -6
• Assertions: +9 / -14
• Skips or known failures added: 0
• Workflow continue-on-error added: 0
• Workflow path filters added: 0
• Test commands removed from justfile: 2
• E2E/journey retry lines added: 0

Coverage risk: likely reduced

Warnings

• Test files deleted (likely reduced)
  • tests/scenario-dev/run.sh
  • tests/scenario-dev/run_sh_test.go
• Test cases removed (likely reduced)
  • 6 removed vs 4 added
• Assertions removed (needs review)
  • 14 removed vs 9 added
• CI/test runner behavior changed (likely reduced)
  • 1 possible workflow job line(s) removed
• Test command removed (likely reduced)
  • 2 test command line(s) removed from justfile
• Files without patch data (needs review)
  • tests/mw-dev/e2e/harness.sh
  • tests/mw-dev/manifests.tmpl.yaml
  • tests/mw-dev/scenario/core/artifacts.go
  • tests/mw-dev/scenario/core/artifacts_test.go
  • tests/mw-dev/scenario/core/catalog.go
  • tests/mw-dev/scenario/core/catalog_test.go
  • tests/mw-dev/scenario/core/runner.go
  • tests/mw-dev/scenario/core/runner_test.go
  • ... and 34 more
• E2E or journey files changed (needs review)
  • tests/e2e-mw-dev/README.md -> tests/mw-dev/README.md
  • tests/e2e-mw-dev/harness.sh -> tests/mw-dev/e2e/harness.sh
  • tests/e2e-mw-dev/manifests.tmpl.yaml -> tests/mw-dev/manifests.tmpl.yaml
  • tests/e2e-mw-dev/run.sh -> tests/mw-dev/run.sh
  • tests/e2e-mw-dev/run_sh_test.go -> tests/mw-dev/run_sh_test.go