chore: triage residual squad/cast-name references after Phase 1 de-squad

[primetimetank21]

Summary

Phase 1 de-squad (#475, #477, #476) removed the embedded .squad/ directory, de-squadded the PR template, and dropped the squad/* branch-naming convention. A post-Phase-1 validation sweep surfaced residual squad/cast-name references that fall outside those three tickets. This issue tracks them for triage — each item below needs a keep/remove decision.

Residual references (from git grep -i squad|jiminy|pluto|mickey|donald|chip|goofy on develop)

1. .copilot/skills/ — 17 SKILL.md files referencing the Squad product (highest priority)

Several skills describe the external Squad product/tooling, not dev-setup functionality:

• release-process/SKILL.md — publishing @bradygaster/squad-cli / @bradygaster/squad-sdk to npm
• architectural-proposals/SKILL.md — SquadUI, squad-interactive-shell
• client-compatibility/SKILL.md — Squad coordinator spawning behavior
• changelog-fold-completeness/SKILL.md — .squad/skills/, sprint retros
• others reference .squad/ paths, Scribe, decisions inbox
  Last touched by chore: de-squad residue scrub (skills, docs, plan artifacts) #478 ("residue scrub"). Decision needed: are these intentionally retained (process skills for an external squad operating on dev-setup) or leftover embedded-squad content to remove/trim?

2. gosquad alias (likely intentional — confirm)

copilot --agent squad --yolo convenience alias:

• README.md:139, config/dotfiles/.aliases:139, config/dotfiles/README.md:86
• scripts/windows/tools/profile.ps1:228-229 (Invoke-CopilotSquad / Set-Alias gosquad)
• tests/test_alias_parity.sh:105 (exclusion-list entry, paired with the above)

3. CONTRIBUTING.md:222,225

SQUAD_WORKTREES=1 worktrees env-var documentation.

4. scripts/linux/setup.sh:89

Code comment: "Apply dotfiles if Pluto's installer exists" (cast-name in a comment).

5. tests/test_windows_setup.ps1:878

N-3: Profile content heredoc includes the squad BEGIN and END markers — profile managed-block marker text still contains "squad".

Out of scope (intentional — keep)

• .mailmap — remaps historical Jiminy/Donald/Mickey/Pluto commit identities to the real author (correct attribution hygiene)
• CHANGELOG.md — entries documenting the de-squad itself + append-only historical records

Acceptance

• Each item 1–5 has an explicit keep/remove decision
• Items marked "remove" are cleaned (ASCII-only, conventional-commit branch, PR to develop)
• git grep -i "squad|jiminy|pluto|mickey|donald|chip|goofy" on develop returns only intentionally-retained references