AFI parity: generate the matrix from conformance probes, not prose

The per-adapter parity table was hand-maintained prose. An adapter that
never wired a capability (FastAPI SSR, Axum WebSocket) got its gap
relabelled "Django-only" or "out of scope — use native equivalents," and
nothing went red. The de-scope was crystallized in five mutually-ratifying
sites: the README §Stack-extensions table, the AFI fixture docstring
("channels/forms/shapes aren't AFI-common"), the core registry's
extension-hook framing, the mizan-fastapi __init__ docstring, and a
"CSRF is Django-only" comment in two adapters' session endpoints.

Replace prose-parity with conformance-generated parity:

- tests/afi/manifest.py declares the AFI-common surface as data — one list
  of capabilities, one of adapters. Applicability ("—") is derived from
  transport, never typed.
- tests/afi/probes.py independently inspects each backend's source for the
  artifact a capability requires (comment-stripped, backend-scoped). Green
  means wired; a cell can't be set by editing a word.
- tests/afi/test_capability_parity.py asserts every (capability × applicable
  adapter) pair is wired. 35 unwired gaps are now loud red TFDD tests, each
  naming an owed binding. No xfail/skip.
- tests/afi/parity_table.py generates the README table from the probes;
  `make parity-check` fails CI on any hand-edit, like the codegen byte-parity.

Purge the five de-scope sites. The IR byte-parity gate is unchanged and green.
`make test-afi` is now intentionally red on the 35 gaps — that board is the
owed parity work, itemized; a gap turns green by being wired, never described.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/afi/fixture.py

@@ -7,7 +7,11 @@ exercise the protocol axes both backends must agree on:
 - two context functions sharing a param (proves bundling + param elevation)
 - a mutation declaring `affects` on the context
 
-No channels, no forms, no shapes — those aren't AFI-common.
+This fixture is deliberately minimal: it exercises the axes the *IR-shape*
+parity test (`test_codegen_parity.py`) needs to compare. It intentionally omits
+channels / forms / shapes — NOT because those are outside the AFI (they are
+AFI-common; see `manifest.py`), but because their per-adapter wiring is gated by
+the *capability* parity suite (`test_capability_parity.py`), not by IR-shape.
 
 `register_fixture()` registers the functions with mizan_core.registry.
 Backend test apps import this module and call register_fixture() during