fix(docs): remove non-existent conversation_entity setting from homeassistant troubleshooting

[liuhao1024]

What does this PR do?

Removes the troubleshooting section referencing a non-existent conversation_entity config setting from the Home Assistant platform adapter documentation. The setting is not implemented in the plugin code and leads to user confusion.

Related Issue

Fixes #48448

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• website/docs/user-guide/messaging/homeassistant.md: Removed the "conversation entity not found" troubleshooting paragraph that references the non-existent conversation_entity setting

How to Test

1. Open website/docs/user-guide/messaging/homeassistant.md
2. Verify the conversation_entity reference is no longer present in the Troubleshooting section
3. Verify the remaining troubleshooting items (env vars, REST auth) are intact
4. Run grep -r "conversation_entity" website/ plugins/ tools/ — should return no results

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features) — N/A (docs-only)
• I've tested on my platform: macOS

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Code Intelligence

• Analyzed: website/docs/user-guide/messaging/homeassistant.md, plugins/platforms/homeassistant/, tools/homeassistant_tool.py
• Blast radius: LOW (documentation-only change, no code affected)
• Related patterns: conversation_entity grep across entire codebase returns 0 hits in .py/.ts files

[teknium1]

Merged via PR #49914 (docs salvage cluster). Your commit was cherry-picked onto current main with your authorship preserved in git log — merged with rebase so it lands under your name. Thanks for the contribution!