docs(l0): declaration grammar moves to .mosaic/repo.json (#1216)

Amendment per operator GO (ms-grill-me design round, 2026-08-20):

- Declaration is .mosaic/repo.json under integration_trunk, not a
  byte-exact AGENTS.md line. Unknown/misspelled keys and unparsable
  files are a structural hard stop; no prose grammar to near-miss
  (Q15 answer, plan D3/D9).
- Changing an existing declaration is operator-owned, above ordinary
  PR review (SF2, plan D10).
- Seeds this repo's declaration: integration_trunk next,
  release_branch main — prevents the absent-declaration default from
  rebinding the stack to main at land time.
- Gloss references in BOOTSTRAP/CODE-REVIEW/CI-CD-PIPELINES point at
  repo.json; merge of origin/next restores pinned-image CI coverage
  for this pre-pin branch (D27 caveat).

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

@@ -5,9 +5,9 @@
 ## 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.
+> in branch conditions and version rules. A project that declares a different trunk in its
+> `.mosaic/repo.json` under `integration_trunk` (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: