Remove the three retired conventions from every AGENTS.md

[lesnik512]

Why

Three paragraphs were pasted into most AGENTS.md files and have since been dropped from the standard: they are process notes, not facts an agent needs before its first edit.

• "Real work not scheduled becomes a GitHub issue" (26 repos)
• the INVARIANT: docstring convention (25 repos)
• the # ty: ignore note (18 repos; ty honours # type: ignore too, and every ty repo already uses # ty: ignore uniformly, so the note enforces nothing)

Change

Delete those paragraphs from each AGENTS.md. Nothing else changes: repos that use INVARIANT: docstrings (modern-di, faststream-outbox) keep them as local practice, and faststream-outbox keeps its test_invariant_census.py.

Done when

grep -l 'not scheduled\|INVARIANT:\|# ty: ignore' */AGENTS.md across the org checkouts returns nothing.