Update self-hosting & migration guides for 0.9.x

[SohamKukreti]

Summary

The self-hosting guide predated the 0.9.0 secure-by-default release and its quickstarts produced an unreachable server. Verified against a fresh 0.9.2 deployment.

Fixes #2090

List of files changed and why

self-hosting.md:

• Require CRAWL4AI_API_TOKEN in every quickstart (docker run, compose, manual build); explain the loopback-only bind and the resulting "connection reset" on published ports, plus startup-delay troubleshooting
• Compose: .llm.env is required; the token must be set inside it (host export is not forwarded to the container)
• Replace the removed inline-Python hooks API (~600 lines) with the declarative hooks reference: CRAWL4AI_HOOKS_ENABLED flag, action table, /hooks/info, and 0.8.x migration notes
• Rewrite /screenshot and /pdf for the artifact flow; note output_path is removed and currently silently ignored
• Fix dashboard URL (/dashboard, not /monitor); document the token bar in the playground and dashboard UIs
• Fix stale versions (0.8.0 -> 0.9.2); drop the SDK function-hooks example

MIGRATION.md:

• Token setup instructions for compose (.llm.env) and docker run (explicit -e form); clarify the loopback failure symptom
• Document CRAWL4AI_HOOKS_ENABLED and the silent failure modes of legacy hooks.code and output_path

.llm.env.example:

• Add CRAWL4AI_API_TOKEN with guidance; add CRAWL4AI_HOOKS_ENABLED

How Has This Been Tested?

Docs were build using mkdocs and visually verified

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added/updated unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes