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>

protocol/mizan-generate/generator/lib/channels.mjs

@@ -0,0 +1,155 @@
+/**
+ * Channels Code Generator
+ *
+ * Generates TypeScript types and React hooks from Channels OpenAPI schema.
+ * Uses openapi-typescript for robust type generation.
+ */
+
+import openapiTS, { astToString } from 'openapi-typescript'
+
+/**
+ * Generate channels TypeScript types using openapi-typescript.
+ */
+export async function generateChannelsTypes(schema) {
+  // Generate types using openapi-typescript
+  const ast = await openapiTS(schema)
+  const typesCode = astToString(ast)
+
+  const lines = [
+    '// AUTO-GENERATED by mizan - do not edit manually',
+    '// Regenerate with: npm run schemas',
+    '',
+    '// ============================================================================',
+    '// OpenAPI Types (generated by openapi-typescript)',
+    '// ============================================================================',
+    '',
+    typesCode,
+    '',
+  ]
+
+  // Extract channel metadata from x-mizan-channels extension
+  const channels = schema['x-mizan-channels'] || []
+
+  if (channels.length > 0) {
+    lines.push('// ============================================================================')
+    lines.push('// Convenience Type Exports')
+    lines.push('// ============================================================================')
+    lines.push('')
+
+    for (const channel of channels) {
+      if (channel.hasParams) {
+        lines.push(`export type ${channel.paramsType} = components["schemas"]["${channel.paramsType}"]`)
+      }
+      if (channel.hasReactMessage) {
+        lines.push(`export type ${channel.reactMessageType} = components["schemas"]["${channel.reactMessageType}"]`)
+      }
+      if (channel.hasDjangoMessage) {
+        lines.push(`export type ${channel.djangoMessageType} = components["schemas"]["${channel.djangoMessageType}"]`)
+      }
+    }
+
+    lines.push('')
+    lines.push('// ============================================================================')
+    lines.push('// Channel Registry')
+    lines.push('// ============================================================================')
+    lines.push('')
+    lines.push('export const CHANNELS = {')
+    for (const channel of channels) {
+      lines.push(`  ${channel.name}: {`)
+      lines.push(`    name: '${channel.name}',`)
+      lines.push(`    pascalName: '${channel.pascalName}',`)
+      lines.push(`    hasParams: ${channel.hasParams},`)
+      lines.push(`    hasReactMessage: ${channel.hasReactMessage},`)
+      lines.push(`    hasDjangoMessage: ${channel.hasDjangoMessage},`)
+      if (channel.hasParams) {
+        lines.push(`    paramsType: '${channel.paramsType}',`)
+      }
+      if (channel.hasReactMessage) {
+        lines.push(`    reactMessageType: '${channel.reactMessageType}',`)
+      }
+      if (channel.hasDjangoMessage) {
+        lines.push(`    djangoMessageType: '${channel.djangoMessageType}',`)
+      }
+      lines.push(`  },`)
+    }
+    lines.push('} as const')
+  } else {
+    lines.push('export const CHANNELS = {} as const')
+  }
+
+  lines.push('')
+
+  return lines.join('\n')
+}
+
+/**
+ * Generate channel hooks from metadata.
+ */
+export function generateChannelsHooks(schema) {
+  const channels = schema['x-mizan-channels'] || []
+
+  if (channels.length === 0) {
+    return null
+  }
+
+  const lines = [
+    "'use client'",
+    '',
+    '// AUTO-GENERATED by mizan - do not edit manually',
+    '// Regenerate with: npm run schemas',
+    '',
+    "import { useChannel, type ChannelSubscription } from 'mizan/channels'",
+    '',
+  ]
+
+  // Collect type imports
+  const typeImports = []
+  for (const channel of channels) {
+    if (channel.hasParams) typeImports.push(channel.paramsType)
+    if (channel.hasReactMessage) typeImports.push(channel.reactMessageType)
+    if (channel.hasDjangoMessage) typeImports.push(channel.djangoMessageType)
+  }
+
+  if (typeImports.length > 0) {
+    lines.push(`import type { ${typeImports.join(', ')} } from './generated.channels'`)
+    lines.push('')
+  }
+
+  // Generate hooks for each channel
+  lines.push('// ============================================================================')
+  lines.push('// Channel Hooks')
+  lines.push('// ============================================================================')
+  lines.push('')
+
+  for (const channel of channels) {
+    const paramsType = channel.hasParams ? channel.paramsType : 'Record<string, never>'
+    const reactMsgType = channel.hasReactMessage ? channel.reactMessageType : 'never'
+    const djangoMsgType = channel.hasDjangoMessage ? channel.djangoMessageType : 'never'
+
+    lines.push(`/**`)
+    lines.push(` * Hook for the ${channel.name} channel.`)
+    lines.push(` */`)
+
+    if (channel.hasParams) {
+      lines.push(`export function use${channel.pascalName}Channel(params: ${paramsType}): ChannelSubscription<${paramsType}, ${djangoMsgType}, ${reactMsgType}> {`)
+      lines.push(`  return useChannel('${channel.name}', params)`)
+    } else {
+      lines.push(`export function use${channel.pascalName}Channel(): ChannelSubscription<Record<string, never>, ${djangoMsgType}, ${reactMsgType}> {`)
+      lines.push(`  return useChannel('${channel.name}', {})`)
+    }
+    lines.push('}')
+    lines.push('')
+  }
+
+  return lines.join('\n')
+}
+
+/**
+ * Generate all channels files.
+ */
+export async function generateChannelsFiles(schema) {
+  const types = await generateChannelsTypes(schema)
+  const hooks = generateChannelsHooks(schema)
+
+  return { types, hooks }
+}