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/CONTRACT.md

@@ -239,7 +239,8 @@ that layer is named GTD rather than folded into `wiki-`), and `stack-` for the s
 development, nested under `instructions/dev/` and therefore never present in a distributed
 instance (`instructions/dev/` above).
 <!-- dist:strip-start -->
-Dev-instance-only: the two skills in that family today are `stack-dev` and `stack-close`.
+Dev-instance-only: the three skills in that family today are `stack-dev`, `stack-build` and
+`stack-close`.
 <!-- dist:strip-end -->
 A new skill takes the prefix of the family it belongs to, or opens a new one deliberately - never
 a bare name.
@@ -350,8 +351,8 @@ symmetry: every other skill's flow is short enough, and fails loudly enough step
 reader cannot lose the thread even without a checklist - `wiki-manage`'s two flows, `wiki-query`,
 `wiki-status` and `gtd-weekly-review` all clear that bar.
 <!-- dist:strip-start -->
-Dev-instance-only: `stack-dev` and `stack-close` sit under the same threshold, for the same
-reason.
+Dev-instance-only: `stack-dev`, `stack-build` and `stack-close` sit under the same threshold,
+for the same reason.
 <!-- dist:strip-end -->
 
 None of this is counted by number on purpose: a per-skill step count is a claim about a file this