docs(sc-gh-stacks): web-UI stack merge is sanctioned for humans, not a workaround

Field-confirmed: GitHub's UI stack merge is the same native flow gh stack
merge drives (bottom layers land, upper PRs retarget automatically). Only
gh pr merge retries and hand-rolled REST remain forbidden; agents use
gh stack merge <pr#> --yes.

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

Author: randlee

packages/sc-gh-stack/skills/managing-gh-stacks/SKILL.md

@@ -8,10 +8,10 @@ description: >
   dependency graph onto stacks and worktrees, convert several existing PRs into
   one stack, keep a stack cleanly rebased as fixes merge into middle layers, or
   land a whole stack in one CI cycle. Also use when GitHub refuses a normal
-  merge because a PR is "part of a stack" — never work around that with
-  `gh pr merge`, the web UI, or raw REST calls. Read this before running any
-  `gh stack` command — the tool is new, blocks under a PTY, and cannot be
-  driven from prior knowledge.
+  merge because a PR is "part of a stack" — the answer is `gh stack merge`,
+  never retrying `gh pr merge` or hand-rolling REST calls. Read this before
+  running any `gh stack` command — the tool is new, blocks under a PTY, and
+  cannot be driven from prior knowledge.
 ---
 
 # Managing gh Stacks
@@ -113,7 +113,7 @@ one agent per stack:
 | Task graph → parallel dev plan | `sc-stack-plan` | tasks, trunk, repo_root | stacks + worktree creation commands + open questions |
 | Flat PRs → one stack | `sc-stack-convert` | trunk, layers (bottom→top), repo_root | decision log: branches before/after/pushed, resolutions, surfaced conflicts |
 | Trunk moved / mid-stack fix merged | `sc-stack-sync` | worktree, fix_branch? | decision log: same contract |
-| `gh pr merge` refused: PR is "part of a stack" | none — run `gh stack merge <pr#> --yes` | — | merges that PR and every unmerged PR below it, atomically; never fall back to raw REST or the web UI |
+| `gh pr merge` refused: PR is "part of a stack" | none — run `gh stack merge <pr#> --yes` | — | merges that PR and every unmerged PR below it, atomically; PRs above retarget automatically. Never hand-roll REST calls. (GitHub's web UI stack merge is the same native flow — fine for humans, not agent-drivable.) |
 
 Read `references/playbook-graph-to-stacks.md`, `references/playbook-convert.md`, or
 `references/playbook-sync.md` first — each is a worked example including the agent prompt and