feat(proxy): allow opting out of tier zero

[germondai]

Summary

• add opt-in MITM_PROXY_ALWAYS_SCRAPE configuration
• bypass the MITM direct Tier 0 probe and enter the existing scraper ladder immediately
• preserve the existing challenge-cache bypass and direct WebSocket relay behavior
• expose the setting through every supplied Compose file
• document the distinction from scraper Tier 1 and warn that always-scrape bypasses media and large-file streaming

Verification

• bun run verify
• 360 tests passed
• lint, typecheck, web build, and docs build passed

Fixes #93