Retire the old build spec, and point every reference at the architecture (M0.1)

Development Plan M0.1. Every section reference in code, tests, specs/,
the example config, the tuning guide, and the CLAUDE.md and README files
now cites docs/Architecture.md (P, L, D, O, X, Q) instead of the old
spec's A-H, and docs/Architecture-Build-Spec.md is deleted (git keeps
it). The plan's old-to-new table goes with it.

Mostly mechanical, with a per-site choice where one old section split:
A4 became L2 where it meant stop/abandon/the loop and L3 where it meant
approvals; A10 became L6 in the context-budget code and L7 elsewhere; B2
became D4 for outbound Gitea and publishing and D5 for review intake;
'A3 step N' became the matching step of L8's boot sequence. Comments
describing behaviour the architecture drops (planning always escalating,
thresholds tuned at an old build step) now describe the current code and
point at the Development Plan.

docs/Architecture.md gains one line the rewrite missed: intake outages
delay but never fail work (old B2), now in L5, where the poller and
Matrix code cite it.

Comments and docs only; no behaviour change.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPQ14L3LikyefCMFBqEbKE

nisse-dev/tests/test_expert.py

@@ -109,7 +109,7 @@ def test_consult_is_stateless_and_uses_the_consultant_role(
     desk(client, store).ask("Is this API deprecated?")
 
     call = client.calls[0]
-    # A14: no repo access, no session state — exactly the question, and none
+    # L9: no repo access, no session state — exactly the question, and none
     # of the log the caller was working from.
     assert [e.event.text for e in call["events"]] == ["Is this API deprecated?"]
     assert all("secret repo context" not in e.event.text for e in call["events"])
@@ -131,7 +131,7 @@ def test_retry_succeeds_after_a_bad_first_reply(store: StateStore) -> None:
 
 
 def test_consults_are_recorded_as_composite_events(store: StateStore) -> None:
-    # A16 wants a consult/delegation eval set; reusing the pair gets consult
+    # L9 wants a consult/delegation eval set; reusing the pair gets consult
     # evaluation for free.
     desk(ScriptedClient([GOOD]), store).ask("q")
     events = [e.event for e in store.read_events()]
@@ -183,4 +183,4 @@ def test_budget_counts_only_after_the_task_marker(store: StateStore) -> None:
 
 
 def test_default_budget_is_small() -> None:
-    assert DEFAULT_BUDGET <= 5  # A14: do not let this become a second subsystem
+    assert DEFAULT_BUDGET <= 5  # L9: do not let this become a second subsystem