docs(agents): add Clean Code, minimal-comments, and ASD-STE100 conventions

[jonpspri]

Related Issue

Style policy set directly by the maintainer (process/docs change, no bug or feature).

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Summary

Adds two sets of conventions to AGENTS.md:

Code conventions (new first bullets):

• Coding standards align with Robert C. Martin's Clean Code - intention-revealing names, small functions that do one thing, few arguments, no duplication, boring control flow over cleverness.
• Keep comments to a minimum - code is its own documentation. Comment only what code cannot express (a security invariant, a non-obvious external contract); delete comments that restate the code.

Writing conventions (new section):

• Project writing (README, USER_README, docs/, user-facing prose) complies with ASD-STE100 Simplified Technical English: approved words, short sentences, one instruction per sentence, active voice, present tense, one term per concept, procedures as numbered steps.

Existing conventions (import grouping, logging) unchanged.

Note: this PR and #10 touch different sections of AGENTS.md; either merge order works without conflict.

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Reviewability

• This PR has one clear purpose
• The linked issue is not labeled triage
• Unrelated bugs or improvements are tracked in separate issues/PRs
• Tests are included with the code they validate (docs-only; N/A)

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Type of Change

• Documentation

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Verification

Check	Command	Status
Tests	pytest	N/A (docs-only)
Lint	ruff check .	N/A
Type check	mypy src/	N/A

Manual: reviewed rendered diff; section structure and bullet style match the existing document.

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Checklist

• Tests added/updated for changes and pytest passes (N/A docs-only)
• ruff check . and mypy src/ are green (N/A docs-only)
• Documentation updated
• Commits signed off (git commit -s, DCO)
• No secrets, credentials, or private keys committed