Build mizan-fastapi MVP — HTTP RPC + context bundling

The Blazr-critical surface for FastAPI. Forms, Channels, Shapes, SSR,
and MWT are out of scope (Ryth's call: defer until Blazr exercises
them; FastAPI projects use native equivalents anyway).

What ships:
- POST /api/mizan/call/      RPC dispatch with Pydantic input validation
- GET  /api/mizan/ctx/{name}/ bundled context fetch (all functions in
                              the named context, parallel-evaluated, single
                              JSON response)
- JSON-body invalidation transport (the 'invalidate' field on mutation
  responses, with auto-scoping when mutation arg names match context params)
- Auth check infrastructure expecting request.state.user populated by
  FastAPI middleware/deps (matches FastAPI idioms)
- Cache-Control: no-store on all responses

Built on existing mizan-core: registry (function lookup, context groups,
invalidation metadata), client.function (the @client decorator + ServerFunction
+ _FunctionWrapper). No code copied or duplicated from mizan-django — the
shared substrate is genuinely shared.

Package layout:
  backends/mizan-fastapi/
    pyproject.toml         distribution=mizan-fastapi, module=mizan_fastapi
    src/mizan_fastapi/
      executor.py          dispatch + auth + invalidation
      router.py            FastAPI APIRouter with the two endpoints
    tests/test_dispatch.py 11 e2e tests against TestClient

Test fixture establishes the registration pattern: explicit
register(fn_class, "name") after each @client. mizan-fastapi doesn't
ship discovery — apps register their functions explicitly. (mizan-django
keeps its DjangoAppVisitor discovery; FastAPI's lack of an app system
makes auto-discovery less natural.)

Makefile: install + test targets now include mizan-fastapi alongside
the other packages. New test-core / test-fastapi targets added for
symmetry.

Verified:
- mizan-core: 15/15
- mizan-django: 348 pass, 21 skip, 0 fail
- mizan-fastapi: 11/11
- mizan-ts edge-compat: 34/34

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

backends/mizan-fastapi/src/mizan_fastapi/__init__.py

@@ -0,0 +1,30 @@
+"""
+mizan-fastapi — FastAPI backend adapter for the Mizan protocol.
+
+Provides HTTP RPC dispatch and context bundling on top of mizan-core's
+function registry. Channels, Forms, Shapes, SSR are out of scope for
+the FastAPI adapter — FastAPI projects use native equivalents (WebSocket,
+Pydantic models, ORM-of-choice, server-side rendering frameworks).
+
+Usage:
+    from fastapi import FastAPI
+    from mizan_fastapi import router as mizan_router
+
+    app = FastAPI()
+    app.include_router(mizan_router, prefix="/api/mizan")
+
+    # Register your @client-decorated functions
+    from mizan_core.client.function import client
+    from .my_functions import *  # noqa
+"""
+
+from .router import router
+from .executor import execute_function, ErrorCode, FunctionError, FunctionResult
+
+__all__ = [
+    "router",
+    "execute_function",
+    "ErrorCode",
+    "FunctionError",
+    "FunctionResult",
+]