fix(#4554): trim execute-plan.md 21 bytes under its DEFAULT size-tier cap

gsd-core/workflows/execute-plan.md sat 21 bytes over its own DEFAULT-tier
hard cap (40,960 bytes, tests/workflow-size-budget.test.cjs, ADR-1610) at
next@a27cb6b2fa — introduced by #4540's call-site wiring for the summary.md/
user-setup.md .compact.md variants, which nobody caught crossing this exact
margin before merge. This trips next's own Tests run on every shard/OS
combination, which in turn blocks the repo's Base branch health PR gate
(#4422/#4428) for every open and future PR regardless of that PR's own diff.

Two meaning-preserving trims in the <success_criteria> block: a repeated
parenthetical ("— unless parallel mode (orchestrator handles)", appearing
twice) replaced with a "— same exception" back-reference on its second
occurrence, and one redundant qualifier ("prominently") dropped — its
behavioral content (surface the USER-SETUP.md warning at the TOP of output)
is already fully specified earlier in the same file. 40,981 -> 40,940 bytes,
20 bytes of headroom under the cap. No procedural content lost.

Fixes #4554.

Emitted-Drift-Ack-Hash: gsd-core/workflows/execute-plan.md — deliberate content trim to clear the DEFAULT size-tier cap (#4554); not a regeneration artifact, a hand-authored byte reduction.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

gsd-core/workflows/execute-plan.md

@@ -602,7 +602,7 @@ All routes: `/clear` first for fresh context.
 - USER-SETUP.md generated if user_setup in frontmatter
 - SUMMARY.md created with substantive content
 - STATE.md updated (position, decisions, issues, session) — unless parallel mode (orchestrator handles)
-- ROADMAP.md updated — unless parallel mode (orchestrator handles)
+- ROADMAP.md updated — same exception
 - If codebase map exists: map updated with execution changes (or skipped if no significant changes)
-- If USER-SETUP.md created: prominently surfaced in completion output
+- If USER-SETUP.md created: surfaced in completion output
 </success_criteria>