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/Cargo.lock

@@ -117,6 +117,12 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "cfg-if"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
+
 [[package]]
 name = "clap"
 version = "4.6.1"
@@ -214,6 +220,17 @@ version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
 
+[[package]]
+name = "kdl"
+version = "6.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "81a29e7b50079ff44549f68c0becb1c73d7f6de2a4ea952da77966daf3d4761e"
+dependencies = [
+ "miette",
+ "num",
+ "winnow 0.6.24",
+]
+
 [[package]]
 name = "libm"
 version = "0.2.16"
@@ -226,6 +243,16 @@ version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8ca58f447f06ed17d5fc4043ce1b10dd205e060fb3ce5b979b8ed8e59ff3f79"
 
+[[package]]
+name = "miette"
+version = "7.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5f98efec8807c63c752b5bd61f862c165c115b0a35685bdcfd9238c7aeb592b7"
+dependencies = [
+ "cfg-if",
+ "unicode-width",
+]
+
 [[package]]
 name = "mime"
 version = "0.3.17"
@@ -256,6 +283,7 @@ dependencies = [
  "askama",
  "clap",
  "indexmap",
+ "kdl",
  "serde",
  "serde_json",
  "toml",
@@ -271,6 +299,70 @@ dependencies = [
  "minimal-lexical",
 ]
 
+[[package]]
+name = "num"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "35bd024e8b2ff75562e5f34e7f4905839deb4b22955ef5e73d2fea1b9813cb23"
+dependencies = [
+ "num-bigint",
+ "num-complex",
+ "num-integer",
+ "num-iter",
+ "num-rational",
+ "num-traits",
+]
+
+[[package]]
+name = "num-bigint"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5e44f723f1133c9deac646763579fdb3ac745e418f2a7af9cd0c431da1f20b9"
+dependencies = [
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "num-complex"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73f88a1307638156682bada9d7604135552957b7818057dcef22705b4d509495"
+dependencies = [
+ "num-traits",
+]
+
+[[package]]
+name = "num-integer"
+version = "0.1.46"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7969661fd2958a5cb096e56c8e1ad0444ac2bbcd0061bd28660485a44879858f"
+dependencies = [
+ "num-traits",
+]
+
+[[package]]
+name = "num-iter"
+version = "0.1.45"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1429034a0490724d0075ebb2bc9e875d6503c3cf69e235a8941aa757d83ef5bf"
+dependencies = [
+ "autocfg",
+ "num-integer",
+ "num-traits",
+]
+
+[[package]]
+name = "num-rational"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f83d14da390562dca69fc84082e73e548e1ad308d24accdedd2720017cb37824"
+dependencies = [
+ "num-bigint",
+ "num-integer",
+ "num-traits",
+]
+
 [[package]]
 name = "num-traits"
 version = "0.2.19"
@@ -412,7 +504,7 @@ dependencies = [
  "serde_spanned",
  "toml_datetime",
  "toml_write",
- "winnow",
+ "winnow 0.7.15",
 ]
 
 [[package]]
@@ -433,6 +525,12 @@ version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"
 
+[[package]]
+name = "unicode-width"
+version = "0.1.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7dd6e30e90baa6f72411720665d41d89b9a3d039dc45b8faea1ddd07f617f6af"
+
 [[package]]
 name = "utf8parse"
 version = "0.2.2"
@@ -454,6 +552,15 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "winnow"
+version = "0.6.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c8d71a593cc5c42ad7876e2c1fda56f314f3754c084128833e64f1345ff8a03a"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "winnow"
 version = "0.7.15"