feat(tools): restore squad-cli as a default-installed tool

[primetimetank21]

Summary

Restores @bradygaster/squad-cli as a default-installed tool (#487), reversing the over-scrub from PR #475.

squad-cli is a dev tool (engine behind gosquad='copilot --agent squad --yolo'), not squad coordination infrastructure. Same class of over-scrub as the gosquad removal reversed in PR #478.

Closes #487

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What Changed

Installers (new)

• scripts/linux/tools/squad-cli.sh -- version-aware, sources nvm, timeout 10 on version detect, --no-fund --no-audit, soft-fail (log_warn + exit 0) if npm absent
• scripts/windows/tools/squad-cli.ps1 -- version-aware, soft-fail (Write-Warn + return) if npm absent, ASCII-only (PS 5.1 safe)

Version pin

• .tool-versions: squad-cli 0.10.0 (npm latest stable)

Orchestrator wiring

• scripts/linux/setup.sh: run_tool "squad-cli" added immediately after run_tool "copilot-cli"
• scripts/windows/setup.ps1: dot-source + Install-SquadCli call added immediately after Install-CopilotCli in Main()

Tests

• tests/test_nvm_bootstrap.sh: T7-T9 (nvm sourcing, version pin, idempotency check for squad-cli.sh)
• tests/test_windows_setup.ps1: Group HH (HH-1 through HH-4) -- function existence, Get-ToolVersion usage, ordering in Main, soft-fail guard
• .github/workflows/e2e-install.yml: squad --version assertion added to linux, macos, and windows e2e jobs

Docs

• README.md: squad-cli row in tools table, squad-cli.sh in repo structure diagram, Windows tools count bumped to 10

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Key Decisions (locked)

• Install by default: yes
• Version: 0.10.0 (npm latest; 0.9.4 was the prior pin)
• PS soft-fail: Write-Warn + return if npm absent (not exit 1)
• Insertion point: after copilot-cli (last npm-chain tool) on both platforms
• Out of scope: no embedded .squad/ tree, no squad workflows, no spawn scripts

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Local Verification

• All Group HH tests pass (4/4)
• squad-cli.ps1 parses clean (AST), ASCII-only verified
• squad-cli.sh passes shellcheck (pre-commit hook)
• Changeset: exactly 9 files (2 new installers + 7 edits)

Not locally exercisable (no npm/nvm in this environment): actual npm install, squad --version live output, e2e job assertions. Kix to verify in CI.