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>

backends/mizan-fastapi/README.md

@@ -108,9 +108,8 @@ anonymous request. The executor branches on those for `auth=True`,
 
 ## Generate the frontend
 
-The codegen lives in `backends/mizan-django/generate/` (the codegen package
-is framework-agnostic; the directory name is historical). Point a config at
-your FastAPI app and run the CLI:
+The codegen is `mizan-generate` (in `protocol/mizan-generate/`). Point a
+config at your FastAPI app and run the CLI:
 
 ```js
 // frontend/fastapi.config.mjs
@@ -133,7 +132,7 @@ export default {
 ```
 
 ```bash
-node path/to/mizan-django/generate/generator/cli.mjs --config fastapi.config.mjs
+npx mizan-generate --config fastapi.config.mjs
 ```
 
 The codegen drives `python -m mizan_fastapi.cli <module>` under the hood,