fix: [#86] Improve trae-cli installation docs and troubleshooting

[nandanosql]

Fixes #86

Problem

After installing trae-agent with uv sync, running trae-cli directly produces "command not found" because the virtual environment bin directory is not on PATH by default.

Solution

Expanded the troubleshooting section in README.md with three clear approaches to running trae-cli:

1. Activate the virtual environment (source .venv/bin/activate)
2. Use uv run (no activation needed)
3. Call the binary directly (.venv/bin/trae-cli)

Also added a tip about persisting venv activation in shell profile for convenience.

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