feat: add [MANUAL] notation for human interaction steps

[Bortlesboat]

Summary

• Add [MANUAL] prefix to help text and runtime messages for commands requiring human interaction
• Helps AI agents identify when to hand control back to the user
• Implements Phase 1 of Add [MANUAL] notation for steps requiring human interaction #66

Changes

• auth_commands.rs: login and setup commands marked [MANUAL] in help text; browser-open prompt prefixed with [MANUAL]
• setup.rs: OAuth consent screen setup instructions prefixed with [MANUAL] for each manual step; browser login step marked
• skills/gws-shared/SKILL.md: Auth section documents which methods are [MANUAL] vs automated

Design

Following the issue's spec, [MANUAL] is:

• Simple and grep-able (grep -r '\[MANUAL\]')
• Parseable by both humans and AI agents
• Placed at the start of the relevant line/step

Phase 2 (structured JSON hint objects) is left for a follow-up PR.

Addresses #66

Test plan

• [MANUAL] annotations are grep-able in help output
• cargo test passes (CI will verify)
• cargo clippy -- -D warnings clean (CI will verify)

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[changeset-bot]

🦋 Changeset detected

Latest commit: f779fab

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@googleworkspace/cli	Minor

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[Bortlesboat]

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[codecov]

Codecov Report

❌ Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.19%. Comparing base (c6095dd) to head (f779fab).
⚠️ Report is 27 commits behind head on main.

Files with missing lines	Patch %	Lines
src/error.rs	0.00%	3 Missing ⚠️
src/auth_commands.rs	66.66%	1 Missing ⚠️
src/setup.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #110   +/-   ##
=======================================
  Coverage   56.19%   56.19%           
=======================================
  Files          38       38           
  Lines       13860    13860           
=======================================
  Hits         7788     7788           
  Misses       6072     6072           

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