fix: prevent stderr output that causes TUI ghost text

[Antonio-Bennett]

Summary

• Replace all console.error() in hooks with client.app.log() (OpenCode's structured logger)
• Set explicit dtype: 'q8' in embedder pipeline to prevent @huggingface/transformers warning
• Set TRANSFORMERS_VERBOSITY=error as safety net for any remaining transformers stderr

Problem

OpenCode TUI renders plugin stderr into the input area, causing ghost text overlapping user input. Two sources:

1. console.error() calls in src/hooks.ts (8 occurrences)
2. @huggingface/transformers dtype warning from src/embedder.ts

Changes

• src/hooks.ts: console.error() → client.app.log(), thread client param into onSessionDeleted
• src/index.ts: pass client to onSessionDeleted
• src/embedder.ts: add dtype: 'q8' + TRANSFORMERS_VERBOSITY=error

Tested locally — no more ghost text in TUI after these changes.