[DOCS] get-started/ai-assistant: replace the third-party NEO prompt file with the fhenix-toolkit plugin (DOC-27)

[alexandrecarvalheira]

Closes DOC-27.

Problem

The AI assistant page told readers to load a third-party core.md from a community repository into their assistant. That file is frozen at an old API: it teaches the removed FHE.decrypt flow, the old input types, and a type that does not exist, so it trains assistants to produce obsolete code.

Fix

The page now documents fhenix-toolkit, Fhenix's own Claude Code plugin, as requested on the card:

• What it is and why it stays current: concepts and gotchas live in the plugin, while API surfaces are looked up live from the public repositories.
• Install steps for the terminal and the desktop app, taken from the repository README and checked against the marketplace and plugin manifests (both named fhenix-toolkit, version 0.2.0).
• A table of the four skills (fhenix-contracts, fhenix-sdk, fhenix-review, fhenix-tests) and the fhe-reviewer subagent, matching the repository tree.
• A section for readers on other assistants: load the plugin's SKILL.md files as context, or use the open-in-ChatGPT/Claude/Cursor menu every docs page already has (the contextual options in docs.json).
• Status (public, pre-1.0) and where to report issues.

The page keeps its ai-assistant slug and navigation entry, so no redirect is needed. The emoji, arrows, and untagged code block the linters flagged on the old page are gone with it.

Verification

• All claims about the plugin come from the repository's README, file tree, and manifests as of today.
• scripts/lint-docs.py and Vale 3.9.6 report zero errors and zero warnings on the page.

🤖 Generated with Claude Code

https://claude.ai/code/session_01N9U7mbjLRhMbPGW8Zej1PB

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