Test strategy

Sets the levels, the pre-PR command and the rules for flaky tests, and writes them into the "Test strategy" section of docs/sdlc.md.

Steps

1. Find what exists. Test folders, test frameworks in the manifests, the CI jobs that run tests, the last CI runs (gh run list --limit 10). Count tests per level if they are named by level.

2. Pick the levels.

   Level	Covers	Rule
   Unit	One function or module; no network, no clock, no shared state	Most tests live here; each runs in milliseconds
   Integration	The service with its real database, queue or file system, in containers	One per external dependency and per main path
   End to end	A user path through the deployed system	A handful, on the paths that make money or lose data
   Smoke	The service answers after a deploy	Runs in the deploy job; a failure triggers the rollback