docs: show how to fix PATH for custom npm prefixes in installation troubleshooting

[omercangumus]

What

Replaces the diagnostics-only squad: command not found entry in docs/src/content/docs/get-started/installation.md with the actual fix: npm prefix -g to locate the global bin, then per-platform PATH instructions (shell profile export for macOS/Linux, [Environment]::SetEnvironmentVariable for Windows). Docs-only — no code change.

Why

Fixes #1458

The section said "Fix:" but only showed diagnostic commands, so a user with a custom npm prefix could confirm the problem and still not know what to do about it. The old Windows line was also cmd syntax (echo %PATH% | findstr npm) that errors in PowerShell, the default shell the docs otherwise assume.

Testing

• Verified live on Windows 11: npm install -g --prefix <sandbox> @bradygaster/squad-cli against the published package — the squad.cmd shim lands directly in the prefix root, no bin\ subdirectory, which is why the doc now spells out the macOS/Linux vs Windows split
• The PowerShell snippet's [Environment]:: calls syntax-checked with an ephemeral process-scope variable; the real 'User'-scope write was not run against this machine's PATH, by design
• The bash export line dry-run in a subshell — $(npm prefix -g)/bin resolves and prepends as written
• npm run lint:docs (markdownlint + cspell) — 0 errors
• git diff vs git diff -w identical; file stays LF

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⚠️ Quick Check

• No changeset — docs-only change, no governed source/template paths touched

PR Readiness Checklist

Branch & Commit

• Branch created from dev
• Branch is up to date with dev
• Verified diff contains only intended changes (single docs file, +21 −4)
• PR is not in draft mode
• Commit history is clean (single commit)

Build & Test

• npm run lint:docs passes
• Build/tests N/A — no code changed

🤖 Generated with Claude Code

[github-actions]

🟢 Impact Analysis — PR #1488

Risk tier: 🟢 LOW

📊 Summary

Metric	Count
Files changed	1
Files added	0
Files modified	1
Files deleted	0
Modules touched	1

🎯 Risk Factors

• 1 files changed (≤5 → LOW)
• 1 module(s) touched (≤1 → LOW)

📦 Modules Affected

docs (1 file)

• docs/src/content/docs/get-started/installation.md

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This report is generated automatically for every PR. See #733 for details.

[github-actions]

🛫 PR Readiness Check

ℹ️ This comment updates on each push. Last checked: commit 67279e6

PR Scope: 🔧 Infrastructure

⚠️ 2 item(s) to address before review

Status	Check	Details
✅	Single commit	1 commit — clean history
✅	Not in draft	Ready for review
✅	Branch up to date	Up to date with dev
❌	Copilot review	No Copilot review yet — it may still be processing
✅	Changeset present	No source files changed — changeset not required
✅	Scope clean	No .squad/ or docs/proposals/ files
✅	No merge conflicts	No merge conflicts
✅	Copilot threads resolved	No Copilot review threads
❌	CI passing	5 check(s) still running

Files Changed (1 file, +21 −4)

File	+/−
docs/src/content/docs/get-started/installation.md	+21 −4

Total: +21 −4

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This check runs automatically on every push. Fix any ❌ items and push again.
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[tamirdresher]

Closing in favor of #1459, which now covers the same PATH troubleshooting problem and includes the more complete User PATH handling, duplicate prevention, whitespace trimming, and separate bash/zsh guidance. Thank you for the contribution and review work here.