Mizan-Rust backend adapter: server-side substrate + three-way parity

Adds first-class Rust-backed Mizan to sit alongside mizan-django and
mizan-fastapi. A Rust dev writes:

    #[derive(Mizan, Serialize, Deserialize)]
    pub struct ProfileOutput { pub user_id: i64, pub name: String }

    #[mizan::context("user")]
    pub struct UserCtx;

    #[mizan::client(context = UserCtx)]
    pub async fn user_profile(_req: &RequestHandle<'_>, user_id: i64) -> ProfileOutput { ... }

…and gets byte-identical KDL to the Python emitters, served over the
same wire protocol the React / Rust / Vue / Svelte kernels speak.

New crates:
- cores/mizan-rust/         (Cargo: mizan-core)     — IR types, KDL emitter, traits, registry,
                                                       runtime (compute_invalidation / compute_merges
                                                       ported from mizan-fastapi), graph_check with
                                                       structural type-matching
- cores/mizan-rust-macros/  (Cargo: mizan-macros)   — #[derive(Mizan)], #[mizan::context],
                                                       #[mizan::client] proc macros
- backends/mizan-rust-axum/ (Cargo: mizan-axum)     — axum HTTP adapter: /session/, /call/, /ctx/:name/
- tests/afi/rust_app/                                — AFI fixture port + server / export-ir binaries

Substrate-shape moves required by cross-language equivalence:
- IR canonicalization: functions / contexts / context-members / shared-by
  now sort alphabetically in both Python and Rust emitters. The IR is a
  contract; linkme doesn't preserve declaration order, so canonical sort
  is the only stable mapping. afi_ir.kdl + per-target baselines regenerated.
- MizanType::TYPE_NAME is a const (with a default type_name() reader) so
  it's usable in linkme TypeEntry static initializers.
- Tree-shaken type registry: #[derive(Mizan)] only emits the trait impl;
  the #[mizan::client] macro registers canonical-named entries from
  fn signatures, including Vec<T> element types for ref resolution.
- Merge resolution is structural (NamedType shape comparison) rather than
  by name — matches the Python types_match_for_merge semantics.

Three-way forcing functions:
- tests/afi/test_codegen_parity.py — Django ≡ FastAPI ≡ Rust on KDL bytes (3 pass)
- tests/rust/run_wire_parity.py    — 12/12 probes against FastAPI + Rust (EXIT=0)

Incidental fixes surfaced by the new tests:
- Stale `from .registry import validate_registry` import removed from
  mizan-django/setup/discovery.py (referenced a function that no longer
  exists; was masking codegen-parity).
- BASE_DIR added to tests/afi/django_app/project/settings.py.
- /session/ endpoint added to mizan-fastapi for protocol-shaped readiness
  probe parity (wire-parity harness now polls /api/mizan/session/ on both
  backends rather than FastAPI's /openapi.json).
- Root .gitignore picks up Rust target/ across the tree so new crates
  don't need per-crate gitignore.

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

cores/mizan-rust-macros/src/lib.rs

@@ -0,0 +1,58 @@
+//! Proc macros for `mizan-core`. See sibling modules for each macro's body.
+//!
+//! Consumer code reads:
+//!   ```ignore
+//!   use mizan_core::prelude::*;
+//!   pub use mizan_core as mizan;  // so `#[mizan::context]` / `#[mizan::client]` read naturally
+//!
+//!   #[derive(Mizan, serde::Serialize, serde::Deserialize)]
+//!   pub struct ProfileOutput { pub user_id: i64, pub name: String }
+//!
+//!   #[mizan::context("user")]
+//!   pub struct UserCtx;
+//!
+//!   #[mizan::client(context = UserCtx)]
+//!   pub async fn user_profile(req: &Request, user_id: i64) -> ProfileOutput { ... }
+//!   ```
+//!
+//! The function macro is named `client` to mirror Python's `@client`
+//! decorator and to keep the namespace `mizan::` purely a module path —
+//! `#[mizan(...)]` would collide with `mizan::context` (a module path
+//! can't simultaneously be a callable macro in Rust).
+
+mod context;
+mod derive;
+mod function;
+mod shape;
+
+use proc_macro::TokenStream;
+use syn::{parse_macro_input, DeriveInput, ItemFn, ItemStruct};
+
+#[proc_macro_derive(Mizan)]
+pub fn derive_mizan(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    derive::expand(input).into()
+}
+
+#[proc_macro_attribute]
+pub fn context(attr: TokenStream, item: TokenStream) -> TokenStream {
+    let args = match context::ContextArgs::parse(attr.into()) {
+        Ok(a) => a,
+        Err(e) => return e.to_compile_error().into(),
+    };
+    let item = parse_macro_input!(item as ItemStruct);
+    context::expand(args, item).into()
+}
+
+/// The function-registration attribute macro. Used as `#[mizan::client]`
+/// (no args) or `#[mizan::client(context = X, affects = Y, merge = Z,
+/// websocket, private)]`.
+#[proc_macro_attribute]
+pub fn client(attr: TokenStream, item: TokenStream) -> TokenStream {
+    let args = match function::FunctionArgs::parse(attr.into()) {
+        Ok(a) => a,
+        Err(e) => return e.to_compile_error().into(),
+    };
+    let item = parse_macro_input!(item as ItemFn);
+    function::expand(args, item).into()
+}