A retrieval postmortem template, and a public incident log

[akash-coded]

The problem

docs/40-operations/ has a runbook for a live incident and
nothing for afterwards. The
incident runbook ends
with "write the detection gap down" and there is nowhere to write it.

The proposal

An issue template and docs/40-operations/incident-log.md:

symptom            what a user saw, in their words
first hypothesis   including the wrong one, named
root cause         the mechanism
detection gap      why a user found it before a test did   <- the valuable line
regression test    the test that now fails against the broken state
what we did NOT fix and why

Why the detection gap is the point

Every postmortem template has "root cause". Almost none have "what measurement would have caught
this before a user did", which is the only line that changes what you build next.

This repository has three ready-made entries: #1, #2 and
#7. Backfilling them is a good first contribution.