chore: drop the duplicated package descriptions from root apm.yml

Why: for a local-path marketplace entry, apm treats a root description: as
an override of the package's own apm.yml, reported only at verbose level,
so the "two copies stay identical" rule had no enforcement. Same fix as
2def060 made for version:.

Implementation Notes:
- All six root copies matched their package apm.yml before removal; the
  compiled marketplace.json descriptions are unchanged.
- apm-workflow references now scope the "omit it" advice to local-path
  entries: on a remote entry, version: is the semver range that selects
  the tag, and version: or ref: is required.

Impact: ADR-0021 amended; the package apm.yml is the single source.

ADR: 0021
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/adr/0021-plugin-descriptions-state-a-domain-boundary.md

@@ -18,6 +18,9 @@ file, `.claude-plugin/marketplace.json`. Read the "four generated files" in Cont
 generated files" in Consequences as historical counts, true when written. The blast radius shrank;
 the staleness hazard that motivated this ADR did not.
 
+**Amended 2026-09-16:** the root `marketplace.packages[]` copy of each description was removed; the
+package `apm.yml` is now the single source. See the amendment before Consequences.
+
 ## Context
 
 A plugin's published description is one string authored twice — in `plugins/<name>/apm.yml` and in
@@ -203,6 +206,32 @@ sit inside ADR-0020's tiers; the tier would have been silent through all three f
 string, not a link — and the README's own plugin list carries the same enumeration with the same
 staleness, so this relocates the defect rather than fixing it.
 
+## Amendment (2026-09-16): the root copy is removed — the package `apm.yml` is the single source
+
+The Decision's rule that "the two copies … stay identical" is retired by removing the second copy.
+The six `description:` lines under root `apm.yml`'s `marketplace.packages[]` are deleted, the same way
+`2def060` deleted the six `version:` lines beside them. `plugins/<name>/apm.yml`'s `description:` is
+now the only place a package's published description is authored.
+
+The rule's own justification — "the root entry is what reaches the compiled marketplace" — was true
+only while the root entry set the field. apm's Claude marketplace mapper resolves a local-path entry's
+`description` curator-first: the entry's value wins when present, and when it is absent the value is
+read from the package's own `apm.yml` (`apm_cli/marketplace/output_mappers.py`, the `is_local` branch
+calling `_apply_field_with_precedence` with `source_label="package apm.yml"`). The root copy was
+therefore an override, not a mirror. Nothing enforced the identity rule, and on drift apm silently
+published the root value. Removing the copy removes the drift rather than leaving it unchecked.
+
+All six root copies were byte-identical to their package's `apm.yml` when they were removed. After
+the removal, `apm pack` regenerated `.claude-plugin/marketplace.json` with every `description` unchanged,
+and `apm pack --check-versions --check-clean --dry-run` passes. The consequence for the "unbounded
+obligation" in Context is that a description edit is now one edit, not two. The package version bump
+and the catalog patch bump it earns are unchanged
+(`plugins/kyberforge/.apm/skills/apm-workflow/references/configure.md`).
+
+This applies to local-path (`source: ./…`) entries only. A remote entry has no local package
+`apm.yml` to fall back to. Its `description:`, when set, is still the published text, and when it
+is absent apm uses whatever its best-effort remote metadata fetch returns.
+
 ## Consequences
 
 **Three descriptions are rewritten and the compiled output regenerated.** Eight generated files