Move codegen out of mizan-django: protocol/mizan-generate/

The codegen consumes a schema from any backend and emits typed client
code for any frontend — it doesn't belong inside a backend adapter.
That placement was historical sediment from when there was only a
Django backend; it predates the AFI generalization.

New top-level slot: `protocol/` for protocol-level tooling. Tree is
now:

  backends/    server protocol adapters
  frontends/   client kernel + per-framework adapters
  cores/       shared language-level primitives
  protocol/    protocol-level tooling
  workers/     runtime workers / bridges

Codegen moves to `protocol/mizan-generate/`. Same file layout under
`generator/` (cli.mjs, lib/), preserved via git mv.

Package metadata cleaned up:
- name: "generate" (placeholder) → "mizan-generate"
- description filled in
- type: module (cli.mjs is .mjs ESM, was previously declared "commonjs")
- bin entry added so `npx mizan-generate --config <config.mjs>` works
  once the package is published, instead of `node path/to/cli.mjs`.

Path-reference fixups:
- backends/mizan-django/README.md: `node path/to/...` → `npx mizan-generate`
- backends/mizan-fastapi/README.md: same
- ISSUES.md: file paths in three issue entries
- CLAUDE.md: codegen description + Package Layout section refreshed
  (added protocol/, mizan-fastapi entry, mizan-python entry)
- docs/AFI_ARCHITECTURE.md: Package Layout refreshed identically

Verified codegen runs from new location: regenerated the FastAPI
example harness's api/ output, identical to pre-move.

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

docs/AFI_ARCHITECTURE.md

@@ -10,13 +10,17 @@ Tree organized by role.
 ```
 backends/         server protocol adapters
     mizan-django/    Django adapter
+    mizan-fastapi/   FastAPI adapter (AFI-common scope)
     mizan-ts/        TypeScript adapter (proves the protocol is language-agnostic)
 frontends/        client kernel + per-framework adapters
     mizan-base/      framework-agnostic kernel; owns data, status, error; adapters subscribe
     mizan-react/     React contexts + hooks over the kernel
     mizan-vue/       Vue composables over the kernel
     mizan-svelte/    Svelte stores/runes over the kernel
-cores/            shared language-level primitives (mizan-python forthcoming)
+cores/            shared language-level primitives
+    mizan-python/    @client decorator, registry, MWT, HMAC cache keys
+protocol/         protocol-level tooling
+    mizan-generate/  codegen — schema in, typed client out
 workers/          runtime workers / bridges
     mizan-ssr/       Bun subprocess used by the Django template backend
 ```