docs(team): Add AGENT_GUIDELINES.md — conventions for agents on Stran…

[mkmeral]

Adds team/AGENT_GUIDELINES.md — a compact reference for conventions governing AI agents that interact with Strands repositories.

This is the condensed, team/-format version of the guidelines discussed in #523. It distills the review feedback from that PR (48 comments across 7 reviewers) into a scannable reference that lives alongside DECISIONS.md, TENETS.md, and the other team docs.

Guidelines covered:

• Add Value or Stay Silent — agents act only when they have something concrete to contribute
• Keep It Short — progressive disclosure, no walls of text, no excessive praise
• Approvals Need Reasoning — rejections must justify; approvals calibrate to trust level
• Scope Credentials to the Task — principle of least privilege, never maintainer tokens, think through failure modes broadly
• Throttle Autonomous Activity — human-compatible pace, business hours preferred, limit active open items
• Own What You Deploy — named owner responsible for logs, cleanup, iteration, and kill switch
• Monitor What Agents Do — use existing tools, but visibility is non-negotiable
• Maintainers Can Pull the Cord — immediate disable, no approval needed
• Know That Your Agent Works — validate however makes sense (automated, manual, whatever) before deploying; team buy-in required

Also updates team/README.md to include the new document in the contents table.

Related Issues

Condensed version of the design doc in #523

Type of Change

• New content
• Content update/revision
• Structure/organization improvement
• Typo/formatting fix
• Bug fix
• Other (please describe):

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using npm run dev
• Links in the documentation are valid and working

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