Fix #217: uvx pptagent onboard 启动失败

[JiwaniZakir]

Closes #217

Describe your changes

Moves the deeppresenter.tui.app and deeppresenter.tui.controller imports from module-level in deeppresenter/cli/commands.py to lazy imports inside the tui() function body. Previously, these two imports were evaluated at module load time (lines 20–21), which caused a ModuleNotFoundError whenever any CLI command (onboard, generate, serve, etc.) was invoked in environments where the deeppresenter.tui subpackage was absent or not yet installed. By deferring the imports to the point of use inside tui(), all other commands load successfully regardless of whether the TUI dependencies are present.

Adds deeppresenter/test/test_cli_commands.py with a test (test_tui_not_imported_at_module_level) that parses commands.py via the ast module and asserts no top-level ImportFrom nodes reference deeppresenter.tui, preventing regression.

Issue ticket number and link

Issue #217: #217

Checklist before requesting a review

• I have performed a self-review of my code
• If it is a core feature, I have added thorough tests.

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This PR was created with AI assistance (Claude). The changes were reviewed by quality gates and a critic model before submission.

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