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_catalog.py

@@ -1,4 +1,4 @@
-"""Runtime model discovery (spec A5/A11/A13).
+"""Runtime model discovery (architecture L9).
 
 The point of these tests is that nothing here reads the model's *name*. A
 semantic alias like "remote-architecture" is free to point anywhere, so the
@@ -78,7 +78,7 @@ def test_a_semantic_alias_routes_by_its_provider() -> None:
 
 
 def test_the_same_alias_reroutes_when_it_is_repointed() -> None:
-    # A13: provisionally accept LiteLLM's normalization for a vendor with no
+    # L9: provisionally accept LiteLLM's normalization for a vendor with no
     # native adapter, rather than sending it Anthropic-shaped bodies.
     cat = catalog(entry("remote-architecture", "openai/gpt-6-astra", "openai"))
     normalized, passthrough = object(), object()
@@ -189,7 +189,7 @@ def test_discovery_asks_the_proxy_with_the_token() -> None:
 
 
 def test_pinning_records_what_the_alias_resolved_to() -> None:
-    # An alias may point somewhere else tomorrow; eval history (A16) keyed on
+    # An alias may point somewhere else tomorrow; eval history (L9) keyed on
     # the alias alone would average across whatever it pointed at.
     cat = catalog(entry("remote-architecture", "anthropic/claude-opus-5", "anthropic"))
     pinned = cat.pinned({"planner": "remote-architecture"})