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-python/src/mizan_core/ir.py

@@ -469,7 +469,11 @@ def build_ir() -> str:
         lines.append("")
 
     # ── Functions ──
-    for fn_name, fn_class in functions.items():
+    # Alphabetical by wire name — the IR is a canonical contract, not a
+    # transcript of registration order. Both Python and Rust emitters sort
+    # so byte-equivalence holds across language-backed backends.
+    for fn_name in sorted(functions):
+        fn_class = functions[fn_name]
         meta = getattr(fn_class, "_meta", {})
         if meta.get("private") or meta.get("view_path"):
             continue
@@ -481,8 +485,9 @@ def build_ir() -> str:
         lines.append("")
 
     # ── Contexts ──
-    for ctx_name, fn_names in context_groups.items():
-        _emit_context(root, ctx_name, fn_names)
+    # Alphabetical by context name — same reason as functions above.
+    for ctx_name in sorted(context_groups):
+        _emit_context(root, ctx_name, context_groups[ctx_name])
 
     if context_groups:
         lines.append("")
@@ -541,14 +546,16 @@ def _emit_context(root: _Block, ctx_name: str, fn_names: list[str]) -> None:
         slot["required"] = len(slot["shared_by"]) == len(fn_names)
 
     with root.node("context", _kdl_string(ctx_name)) as block:
-        for fn_name in fn_names:
+        # Members alphabetical — canonical order.
+        for fn_name in sorted(fn_names):
             block.leaf("function", _kdl_string(fn_name))
         for param_name in sorted(param_info):
             slot = param_info[param_name]
             with block.node("param", _kdl_string(param_name)) as param_block:
                 param_block.leaf("type", _kdl_string(slot["type"]))
                 param_block.leaf("required", _kdl_bool(slot["required"]))
-                for sharer in slot["shared_by"]:
+                # `shared-by` follows the same canonical ordering.
+                for sharer in sorted(slot["shared_by"]):
                     param_block.leaf("shared-by", _kdl_string(sharer))