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/oplog.py

@@ -1,4 +1,4 @@
-"""Structured operational logging (spec A9).
+"""Structured operational logging (architecture L12).
 
 One JSON object per line to stderr (journald captures it when running as a
 service). Every event carries the fixed envelope: ts, agent, event, task_id,
@@ -16,7 +16,7 @@ class OpLog:
     def __init__(self, agent: str, stream: TextIO | None = None) -> None:
         self.agent = agent
         # Correlation ID for the enclosing unit of work; the orchestrator sets
-        # it when a unit starts and clears it when the unit ends (A9).
+        # it when a unit starts and clears it when the unit ends (L12).
         self.task_id: str | None = None
         self._stream = stream if stream is not None else sys.stderr