refactor(env): consolidate environment variable system with AsyncLocalStorage rewire

Complete rewrite of environment variable access patterns, consolidating 60+ individual env constant files into grouped getter modules with AsyncLocalStorage-based test rewiring.

Changes:
- Add env/rewire.ts with AsyncLocalStorage-based test isolation
- Add grouped env modules: github.ts, socket.ts, socket-cli.ts, socket-cli-shadow.ts, npm.ts, locale.ts, windows.ts, xdg.ts, temp-dir.ts, test.ts
- Convert all env constants to getter functions using getEnvValue()
- Delete 60+ individual env constant files
- Add comprehensive test suite in test/env/

Author: jdalton

src/env/appdata.ts

@@ -1,10 +1,11 @@
 /**
- * CI environment variable snapshot.
+ * CI environment variable getter.
  * Determines if code is running in a Continuous Integration environment.
  */
 
-import { env } from 'node:process'
-
 import { envAsBoolean } from '#env/helpers'
+import { getEnvValue } from '#env/rewire'
 
-export const CI = envAsBoolean(env['CI'])
+export function getCI(): boolean {
+  return envAsBoolean(getEnvValue('CI'))
+}

src/env/ci.ts

@@ -1,8 +1,10 @@
 /**
- * DEBUG environment variable snapshot.
+ * DEBUG environment variable getter.
  * Controls debug output for the debug package.
  */
 
-import { env } from 'node:process'
+import { getEnvValue } from '#env/rewire'
 
-export const DEBUG = env['DEBUG']
+export function getDebug(): string | undefined {
+  return getEnvValue('DEBUG')
+}