chore(8.0): collapse dead defensive guards + redundant polyfills

Follow-up to the browser/cloud/threading sweep — everything that was guarding
against unreachable runtimes is now dead.

cacheManager.ts: Environment enum + this.environment field removed (only NODE
was reachable). StorageType narrowed to MEMORY + FILESYSTEM. navigator.deviceMemory
and performance.memory paths in detectOptimalCacheSize + detectAvailableMemory
deleted; node:os is the sole source. environmentConfig keeps the index signature
for future per-runtime tuning but only the node slot is wired.

Dead 'typeof window === undefined' guards (the check is always true on 8.0):
paramValidation, structuredLogger, mutex, brainy.ts stats block, and
networkTransport ws-dynamic-import all collapsed. IntegrationLoader's inverse
guard ('!== undefined' returning 'browser') deleted. mutex's createMutex default
type simplified from "(typeof window === 'undefined' ? 'file' : 'memory')" to
plain 'file'.

Redundant TextEncoder/TextDecoder polyfills: Node 22+ ships both as globals.
src/utils/textEncoding.ts deleted (applyTensorFlowPatch was named for a defunct
dep and only re-assigned globals already present). setup.ts collapsed to an
empty stable import target. unified.ts loses its applyTensorFlowPatch re-export.

modelAutoConfig.getModelPath() loses the unreachable trailing fallback now
that isNode() is effectively the only branch the function ever takes.

jsonProcessing.ts left unchanged — its 'typeof document' checks are value-shape
guards on the parsed JSON, not environment detection.

src/brainy.ts

@@ -5231,14 +5231,12 @@ export class Brainy<T = any> implements BrainyInterface<T> {
     // Get system memory info
     let freeMemory = 0
     let totalMemory = 0
-    if (typeof window === 'undefined') {
-      try {
-        const os = require('node:os')
-        freeMemory = os.freemem()
-        totalMemory = os.totalmem()
-      } catch (e) {
-        // OS module not available
-      }
+    try {
+      const os = require('node:os')
+      freeMemory = os.freemem()
+      totalMemory = os.totalmem()
+    } catch (e) {
+      // OS module not available
     }
 
     const stats = {