fix(models): force subscription login + add claude-opus-4-6

Subscription runs were failing with "Invalid API key · Fix external API
key": the claude/codex subscription CLIs inherit the harness environment,
and a stray ANTHROPIC_API_KEY/OPENAI_API_KEY (e.g. a stale key saved in the
web console) made them switch to API-key billing and reject the request.
Strip those vars before spawning the CLI so the subscription login is always
used on the CLI path (API-key users go through the HTTP path, unaffected).

Also register claude-opus-4-6 in the anthropic model list — both the harness
allowlist (so it's no longer auto-corrected to claude-opus-4-8) and the web
console provider list.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/server.js

@@ -102,7 +102,7 @@ const PORT = Number(process.env.NEUROSPLOIT_WEB_PORT || process.env.PORT || 4173
 
 const PROVIDERS = [
   { key: 'anthropic', label: 'Anthropic Claude', kind: 'cli', envKey: 'ANTHROPIC_API_KEY',
-    models: ['claude-opus-5-5', 'claude-opus-5', 'claude-sonnet-5', 'claude-fable-5-1', 'claude-opus-4-8', 'claude-sonnet-4-6', 'claude-haiku-4-5'] },
+    models: ['claude-opus-5-5', 'claude-opus-5', 'claude-sonnet-5', 'claude-fable-5-1', 'claude-opus-4-8', 'claude-opus-4-6', 'claude-sonnet-4-6', 'claude-haiku-4-5'] },
   { key: 'openai', label: 'OpenAI (ChatGPT)', kind: 'cli', envKey: 'OPENAI_API_KEY',
     models: ['gpt-6-astra', 'gpt-6-sol', 'gpt-6-luna', 'gpt-5.6-sol', 'gpt-5.6-terra', 'gpt-5.6-luna', 'gpt-5.5', 'gpt-5.4', 'gpt-5.4-mini', 'gpt-5.3-codex', 'gpt-5.2', 'gpt-5.1', 'gpt-5.1-codex', 'o4'] },
   { key: 'xai', label: 'xAI Grok', kind: 'cli', envKey: 'XAI_API_KEY',