nisse-core: group modules into packages by architecture section

A pure move; behaviour unchanged.

- models (L9, L7): llm, catalog, probe, render, render_anthropic, context
- log (L7, L6): canonical, views
- state (L8): store (was state), reconcile, worker, cancel, dump
- knowledge (L10, L6.4): vault, memory
- conversation (L5): transport, matrix
- execution (L13): ssh (was execution), testing
- authority (P3, P4, L4): actions
- gitea, oplog, envfile stay at the top until each gains a second module.

Every import, monkeypatch target, script and doc reference rewritten.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J5Utyfzw7gF7UhjRDEtjTk

scripts/ci-sshd.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# The throwaway sshd the tests need (nisse_core/testing.py), in a CI job.
+# The throwaway sshd the tests need (nisse_core/execution/testing.py), in a CI job.
 # Skipped when the job's image already has it. Otherwise apt fetches from a
 # kernel.org mirror rather than archive.ubuntu.com, which has been slow
 # enough (a few KB/s) to add minutes to every job.