Mizan IR: cut over to KDL, delete OpenAPI envelope

Replaces the transitional OpenAPI 3.0 + `x-mizan-*` extensions
substrate with the canonical Mizan IR as KDL, per docs/AFI_ARCHITECTURE.md:
"KDL is the contract; everything else (REST envelopes, OpenAPI
documents, framework idioms) is sediment around it."

End-to-end cutover. No transitional path left on main.

Forward direction:
  cores/mizan-python/src/mizan_core/ir.py
    build_ir() walks mizan_core.registry, introspects Pydantic
    models directly (no JSON-Schema indirection), and emits the
    Mizan IR document. The KDL grammar is locked in this file's
    module docstring.

Backends emit KDL:
  backends/mizan-fastapi/src/mizan_fastapi/ir.py
    `python -m mizan_fastapi.ir <module>` — CLI entry point.
  backends/mizan-django/.../management/commands/export_mizan_ir.py
    `manage.py export_mizan_ir` — Django mgmt command.

Codegen consumes KDL:
  protocol/mizan-codegen/Cargo.toml: + kdl = "6"
  protocol/mizan-codegen/src/ir.rs: NamedType { Struct/List/Enum/Alias }
    + TypeShape { Primitive/Ref/List/Optional/Enum/Union } sum types,
    replacing the JsonSchema sprawl. KDL parser walks the
    `kdl::KdlDocument` tree into typed Rust structs.
  protocol/mizan-codegen/src/fetch.rs: subprocess command switches
    to the new IR-export entry points.
  All emit modules (stage1 / react / python / rust / vue / svelte /
    channels) port their type-walkers from JsonSchema to the new
    sum types — case analysis collapses substantially.

Substrate-honesty wins beyond the moat closure:
  - `int | bool` multi-arm unions land as `TypeShape::Union` (was
    silently coerced to "string" before).
  - `<CamelName>Output = list[T]` returns emit as named alias
    types instead of struct-shaped wrappers, so consumer code
    `.map()` works directly on the type.
  - Pydantic field defaults flow through to `default` properties
    in KDL, then back to non-optional shape in every target.

Deleted:
  - backends/mizan-fastapi/src/mizan_fastapi/{cli,schema}.py
  - backends/mizan-django/.../export_mizan_schema.py
  - openapi-bearing half of mizan/export/__init__.py (edge
    manifest generator preserved — separate concern).
  - tests/afi/schema_normalizer.py
  - tests/fixtures/{afi_schema.json, channels_schema.json}
  - tests/fixtures/js_* baseline directories.

Verification:
  - 20 mizan-codegen unit tests green (IR deserialization,
    byte-equivalence parity across stage1/rust/python/react/vue/svelte
    against fresh KDL-driven baselines, channels structural).
  - tests/rust/run_wire_parity.py: 12/12 probes green driving
    the binary end-to-end through KDL.
  - Blazr studio-ui typechecks against the regenerated React client.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

protocol/mizan-codegen/tests/fixtures/baselines/python/__init__.py

@@ -0,0 +1,4 @@
+# AUTO-GENERATED by mizan — do not edit
+
+from .client import MizanClient  # noqa: F401
+from .types import *  # noqa: F401, F403

protocol/mizan-codegen/tests/fixtures/baselines/python/client.py

@@ -0,0 +1,67 @@
+# AUTO-GENERATED by mizan — do not edit
+
+from __future__ import annotations
+
+from collections.abc import Callable
+from typing import Any
+
+# Built from frontends/mizan-rust with `maturin develop --features pyo3`.
+from mizan_rust import PyMizanClient, PyContextSubscription
+
+from .types import *  # noqa: F401, F403
+from .types import BaseModel  # re-import for the synthesized ContextData classes
+
+
+class MizanClient:
+    """Typed Python facade over the PyO3 mizan-rust kernel."""
+
+    def __init__(self, base_url: str, *, session: bool = False,
+                 csrf_cookie_name: str = "csrftoken",
+                 csrf_header_name: str = "X-CSRFToken") -> None:
+        self._inner = PyMizanClient(
+            base_url,
+            session=session,
+            csrf_cookie_name=csrf_cookie_name,
+            csrf_header_name=csrf_header_name,
+        )
+
+    def fetch_user_context(self, user_id: int) -> "UserContextData":
+        raw = self._inner.fetch_context("user", {"user_id": user_id})
+        return UserContextData(**raw)
+    def subscribe_user_context(self, user_id: int,
+                                       callback: Callable[[dict[str, Any]], None]) -> PyContextSubscription:
+        return self._inner.subscribe_context("user", {"user_id": user_id}, callback)
+
+    def call_echo(self, args: EchoInput) -> EchoOutput:
+        raw = self._inner.call("echo", args.model_dump())
+        return EchoOutput(**raw)
+
+    def call_whoami(self) -> WhoamiOutput:
+        raw = self._inner.call("whoami", {})
+        return WhoamiOutput(**raw)
+
+    def call_update_profile(self, args: UpdateProfileInput) -> UpdateProfileOutput:
+        raw = self._inner.call("update_profile", args.model_dump())
+        return UpdateProfileOutput(**raw)
+
+    def call_find_user(self, args: FindUserInput) -> FindUserOutput | None:
+        raw = self._inner.call("find_user", args.model_dump())
+        return FindUserOutput(**raw) if raw is not None else None
+
+    def call_rename_user(self, args: RenameUserInput) -> RenameUserOutput:
+        raw = self._inner.call("rename_user", args.model_dump())
+        return RenameUserOutput(**raw)
+
+    def invalidate(self, context: str) -> None:
+        self._inner.invalidate(context)
+
+    def invalidate_scoped(self, context: str, params: dict[str, Any]) -> None:
+        self._inner.invalidate_scoped(context, params)
+
+
+# ── Context data shapes (per-context bundle) ──────────────────────────────
+
+class UserContextData(BaseModel):
+    """Bundled return of fetch_user_context."""
+    user_profile: UserProfileOutput
+    user_orders: UserOrdersOutput

protocol/mizan-codegen/tests/fixtures/baselines/python/types.py

@@ -0,0 +1,56 @@
+# AUTO-GENERATED by mizan — do not edit
+
+from __future__ import annotations
+
+from typing import Any, Literal
+
+from pydantic import BaseModel
+
+class OrderOutput(BaseModel):
+    id: int
+    user_id: int
+    total: int
+
+class EchoInput(BaseModel):
+    text: str
+
+class EchoOutput(BaseModel):
+    message: str
+
+class FindUserInput(BaseModel):
+    user_id: int
+
+class FindUserOutput(BaseModel):
+    user_id: int
+    name: str
+
+class RenameUserInput(BaseModel):
+    user_id: int
+    name: str
+
+class RenameUserOutput(BaseModel):
+    user_id: int
+    name: str
+
+class UpdateProfileInput(BaseModel):
+    user_id: int
+    name: str
+
+class UpdateProfileOutput(BaseModel):
+    ok: bool
+
+class UserOrdersInput(BaseModel):
+    user_id: int
+
+UserOrdersOutput = list[OrderOutput]
+
+class UserProfileInput(BaseModel):
+    user_id: int
+
+class UserProfileOutput(BaseModel):
+    user_id: int
+    name: str
+
+class WhoamiOutput(BaseModel):
+    email: str
+    authenticated: bool