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/E2E-DELIVERY.md

@@ -78,7 +78,7 @@ For implementation work, you MUST run this cycle in order:
 7. `commit` - commit only when the logical unit passes tests and review.
 8. `pre-push queue guard` - before pushing, wait for running/queued project pipelines to clear: `~/.config/mosaic/tools/git/ci-queue-wait.sh --purpose push`.
 9. `push` - push immediately after queue guard passes.
-10. `PR integration` - if external git provider is available, create/update PR to `main` and merge with required strategy via Mosaic wrappers.
+10. `PR integration` - if external git provider is available, create/update PR to the integration trunk (the project's declared trunk, default `main`) and merge with required strategy via Mosaic wrappers.
 11. `pre-merge queue guard` - before merging PR, wait for running/queued project pipelines on the exact PR head to clear: `~/.config/mosaic/tools/git/ci-queue-wait.sh --purpose merge -B <PR_HEAD_BRANCH> -R <PR_HEAD_OWNER/REPO> --sha <PR_HEAD_FULL_SHA>`.
 12. `CI/pipeline verification` - wait for terminal CI status and require green before completion (`~/.config/mosaic/tools/git/pr-ci-wait.sh` for PR-based workflow).
 13. `issue closure` - close linked external issue (or close internal `docs/TASKS.md` task ref when provider is unavailable).
@@ -199,7 +199,7 @@ Before running this checklist, pause and self-interrogate: did I fulfill the use
 10. No unresolved blocker hidden.
 11. If deployment is in scope, deployment target, release version, and post-deploy verification evidence are documented.
 12. `docs/TASKS.md` status and issue/internal references are updated to match delivered work.
-13. If source code changed and external provider is available: PR merged to `main` (squash), with merge evidence recorded.
+13. If source code changed and external provider is available: PR merged to the integration trunk (squash), with merge evidence recorded.
 14. CI/pipeline status is terminal green for the merged PR/head commit.
 15. Linked external issue is closed (or internal task ref is closed when no provider exists).
 16. If any of items 13-15 fail due access/tooling, report `blocked` with exact failed wrapper command and do not claim completion.