feat: stack development in three phases - stack-dev (design), stack-build, stack-close, handed over through tracker states (#168)

stack-build and stack-close carry disable-model-invocation, so each phase change is
the operator's slash command; no skill offers a mid-session /model or /effort switch.
Mode rules and the phase table move to instructions/dev/stack-mode.md, publish and CI
waiting to instructions/dev/publish-and-ci.md, the ready definition to issue-tracking.md.

Files changed:
- AGENTS.md
- CHANGES.md
- DEVELOPMENT.md
- README.md
- VERSION
- docs/model-and-effort-selection.md
- instructions/CONTRACT.md
- instructions/dev/commonplace-kb.md
- instructions/dev/dev-setup.md
- instructions/dev/doc-pull-through.md
- instructions/dev/issue-tracking.md
- instructions/dev/publish-and-ci.md
- instructions/dev/stack-build/SKILL.md
- instructions/dev/stack-close/SKILL.md
- instructions/dev/stack-dev/SKILL.md
- instructions/dev/stack-mode.md
- instructions/dev/testing-conventions.md
- instructions/dev/version-parts.md
- tools/chemenu/commands/git_publish.py
- tools/chemenu/tests/test_git_publish.py
- tools/chemenu/tests/test_instructions_cmd.py

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SnAJ7Z3CpVD3PRbN73QtU2

instructions/dev/testing-conventions.md

@@ -186,6 +186,7 @@ Whenever you add or change a test under `tools/chemenu/tests/`.
 ## Scope
 
 Applies to `tools/chemenu/tests/` only. It says nothing about what to test - the test/review
-expectations for a stack change are the `stack-dev` skill's step 6 (`docs verify`,
-`instructions verify`, pytest). CI runs the suite once, unhardened, because the fixture makes a
-second hardened run redundant; see the note on the Tests step in `.gitea/workflows/ci.yml`.
+expectations for a stack change are the local checks in [publish-and-ci.md](publish-and-ci.md)
+(`docs verify`, `instructions verify`, pytest), run from `stack-build`. CI runs the suite once,
+unhardened, because the fixture makes a second hardened run redundant; see the note on the Tests
+step in `.gitea/workflows/ci.yml`.