docs: Strengthen style guide enforcement in AGENTS.md

[randomm]

Problem

Developers repeatedly introduce style violations (else statements, destructuring, let instead of const) despite STYLE_GUIDE.md existing. The adversarial review catches these, but it wastes a full review+fix cycle each time.

Solution

Add explicit enforcement section to AGENTS.md:

• Reference STYLE_GUIDE.md as mandatory (not advisory)
• List the top violations to avoid (else, destructuring, let, semicolons)
• Make it clear these are blocking issues, not suggestions

Context

During the current sprint, every single developer task required at least one adversarial fix round for style violations. The PM delegation prompts now include style rules explicitly, but AGENTS.md should reinforce this for all agents.

Acceptance Criteria

• AGENTS.md references STYLE_GUIDE.md as mandatory compliance
• Common violations listed explicitly
• All agents read this before writing code

[randomm]

Implemented in commit e10bca2 — docs(agents): add mandatory style guide compliance section