Add .claude/skills/test-quality and reference it from AGENTS.md (#2993)

AGENTS.md

@@ -45,6 +45,8 @@
 
 ## Testing
 
+- When writing or reviewing tests, conform to `.claude/skills/test-quality/SKILL.md`
+  — it defines the bar for naming, abstraction level, assertions, and determinism.
 - Framework: `uv run --frozen pytest`
 - Async testing: use anyio, not asyncio
 - Do not use `Test` prefixed classes — write plain top-level `test_*` functions.
@@ -129,6 +131,13 @@ changes softened by a backwards-compatibility shim. Include:
 Search for related sections in the migration guide and group related changes together
 rather than adding new standalone sections.
 
+## Documentation
+
+When a change affects public API or user-visible behaviour, update the relevant
+page(s) under `docs/` in the same PR. Docs are organised by topic
+(`tutorial/`, `client/`, `run/`, `advanced/`) — find the page covering the
+feature you touched rather than adding a new one.
+
 ## Formatting & Type Checking
 
 - Format: `uv run --frozen ruff format .`