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/src/nisse_dev/expert.py

@@ -1,23 +1,23 @@
-"""`ask_expert` (spec A14).
+"""`ask_expert` (architecture L9).
 
 The one case delegation does not cover: a question needing no repo access —
 "which of these two approaches is better", "is this API deprecated". A single
 stateless call, a text answer, no session state, no diff application.
 
-Two constraints from A14 shape the implementation:
+Two constraints from L9 shape the implementation:
 
 **Structured output is contracted at the prompt level, not the API level.**
 Vendors differ on JSON mode and schema enforcement, so the answer is parsed and
 validated against a local schema, with one retry. This runs over LiteLLM's
-*normalized* route, which A13 reserves for calls where fidelity is cheap.
+*normalized* route, which L9 reserves for calls where fidelity is cheap.
 
 **A per-task budget**, so a confused executor cannot spend twenty consults
 circling. The count comes from the canonical log rather than a counter in
 memory: it survives a restart, and it is observable from outside the model,
-which is the same reasoning A12 applies to escalation triggers.
+which is the same reasoning L9 applies to escalation triggers.
 
 Consults are recorded as ``delegation_started`` / ``delegation_completed`` with
-role ``consultant``. That is deliberate — A16 wants a "consult/delegation eval
+role ``consultant``. That is deliberate — L9 wants a "consult/delegation eval
 set", and reusing the composite events gets consult evaluation for free rather
 than inventing a parallel record.
 """
@@ -150,7 +150,7 @@ class ExpertDesk:
         last = "no reply"
         for attempt in (1, 2):
             try:
-                # Stateless by design (A14): the question travels as a
+                # Stateless by design (L9): the question travels as a
                 # synthesised message that is never appended to the log, so a
                 # consult neither depends on nor leaks repo context. It cannot
                 # ride in the system prompt alone — the Messages API requires