docs(l0): parameterize hard gates on the project's integration trunk

Per Jason's Option-A ruling on #1216: the constitution supplies the general
framework; the project declares its own flow. Defines the integration trunk
once in CONSTITUTION.md Hard Gates — declared by exactly one
'Integration trunk: <branch>' line in the project's root AGENTS.md, default
'main', value bound by git check-ref-format --branch semantics, malformed or
multiple declarations are a hard stop, one trunk only, no gate relaxation —
and binds gates 5/15, E2E-DELIVERY, CODE-REVIEW, ORCHESTRATOR(-PROTOCOL),
BOOTSTRAP provisioning, and the defaults AGENTS session closure to that term.
CI-CD-PIPELINES YAML examples stay on the default trunk with a substitution
note.

Known mechanized consumer left as tracked follow-up on #1216: pr-merge.sh:133
hardcodes a {main,next} base allowlist — fail-closed (refuses exotic trunks,
cannot misroute), to be parameterized with red-first tests separately.

Refs #1216

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01WYgWocp36goy8hj2ui6ps1

packages/mosaic/framework/guides/CI-CD-PIPELINES.md

@@ -4,6 +4,11 @@
 
 ## Overview
 
+> **Integration trunk:** the YAML examples in this guide use the default integration trunk `main`
+> in branch conditions and version rules. A project that declares a different trunk in its root
+> `AGENTS.md` (see `CONSTITUTION.md` Hard Gates) substitutes its declared trunk wherever `main`
+> appears as the trunk branch.
+
 This guide covers the canonical CI/CD pattern used across projects. The pipeline runs in Woodpecker CI and follows this flow:
 
 ```
@@ -865,7 +870,7 @@ steps:
    ```yaml
    image: git.example.com/org/service@${IMAGE_DIGEST}
    ```
-7. **Test on a short-lived non-main branch first** — open a PR and verify quality gates before merging to `main`
+7. **Test on a short-lived non-trunk branch first** — open a PR and verify quality gates before merging to the integration trunk
 8. **Verify images appear** in Gitea Packages tab after successful pipeline
 
 ## Terminal-Green Full-Step Contract
@@ -906,7 +911,7 @@ For source-code delivery, completion is not allowed at "PR opened" stage.
 
 Required sequence:
 
-1. Merge PR to `main` (squash) via Mosaic wrapper.
+1. Merge PR to the integration trunk (squash) via Mosaic wrapper.
 2. Monitor CI to terminal status:
    ```bash
    ~/.config/mosaic/tools/git/pr-ci-wait.sh -n <PR_NUMBER>
@@ -1112,5 +1117,5 @@ If a project currently uses Verdaccio (e.g., U-Connect at `npm.uscllc.net`), fol
 
 ### Pipeline runs Docker builds on pull requests
 
-- Verify `when` clause on Docker build steps restricts to `branch: [main]`
+- Verify `when` clause on Docker build steps restricts to the integration trunk (`branch: [main]` by default)
 - Pull requests should only run quality gates, not build/push images