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/state.py

@@ -1,4 +1,4 @@
-"""Durable state store (spec A2).
+"""Durable state store (architecture L8).
 
 SQLite in WAL mode with ``synchronous=FULL``: every commit is fsynced, so a
 power cut mid-write can never produce torn state. Every state transition and
@@ -127,7 +127,7 @@ class StateStore:
         migrations: Mapping[int, Migration] = MIGRATIONS,
         oplog: OpLog | None = None,
     ) -> None:
-        # Log emission is owned by the store (A9): the same code path that
+        # Log emission is owned by the store (L12): the same code path that
         # performs a durable write emits its log line, right after commit.
         self.oplog = oplog if oplog is not None else OpLog("nisse-dev")
         self._conn = sqlite3.connect(path, isolation_level=None)
@@ -291,7 +291,7 @@ class StateStore:
         ]
 
     def append_event(self, event: CanonicalEvent) -> int:
-        """Append to the canonical transcript (A10); committed and fsynced
+        """Append to the canonical transcript (L7); committed and fsynced
         before return, like every other durable write."""
         cursor = self._conn.execute(
             "INSERT INTO canonical_events (ts, type, payload) VALUES (?, ?, ?)",
@@ -314,7 +314,7 @@ class StateStore:
         ]
 
     def mark_outcome(self, event_id: int, verdict: str, note: str = "") -> None:
-        """Record whether a delegation or consult was good (A16).
+        """Record whether a delegation or consult was good (L9).
 
         Kept out of the canonical log on purpose: the log is an append-only
         record of what happened, and a verdict is a later judgement about it