Fix critical issues C1-C5, C7, H1, H2, H4, H10

C1+C7: Cache purge now passes user_id and works for view-path
mutations. Extracted _purge_cache_for_invalidation() shared helper
used by both RPC and view-path branches.

C2: initSession retries 3x with backoff. Resets on total failure
so next call tries again instead of permanently broken CSRF.

C3: SSR template backend injects __MIZAN_SSR_DATA__ script tag
with serialized props for client-side hydration.

C4: SSR bridge uses _write_lock to serialize stdin writes from
concurrent Django threads. Prevents JSON interleaving.

C5: SSR bridge registers atexit handler for process cleanup.
No more orphaned Bun processes on Django reload/shutdown.

H1: pendingScoped changed from Map to Array — multiple scoped
invalidations for the same context no longer overwrite.

H2: registerContext uses stableKey() (sorted JSON) instead of
bare JSON.stringify. Property order no longer matters.

H4: Named context providers skip refetch if SSR data exists
(matches global context behavior).

H10: _meta always assigned as fresh dict, preventing shared-dict
mutation across ServerFunction subclasses.

373 Django + 33 React tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/mizan-django/generate/generator/lib/adapters/react.mjs

@@ -106,7 +106,7 @@ export function generateReactAdapter(schema) {
         const deps = paramEntries.map(([pName]) => `params.${pName}`)
         lines.push(`    }, [${deps.join(', ')}])`)
         lines.push('')
-        lines.push(`    useEffect(() => { refetch() }, [refetch])`)
+        lines.push(`    useEffect(() => { if (!data) refetch() }, [data, refetch])`)
         lines.push(`    useEffect(() => registerContext('${ctxName}', params, refetch), [${deps.join(', ')}, refetch])`)
         lines.push('')
         lines.push(`    return <${p}Ctx.Provider value={data}>{children}</${p}Ctx.Provider>`)