Add TUI gate view for serve

[theokeist]

Motivation

• Provide a compact terminal UI for the playful gate output so php pipeflow serve --gate can be used as a simple TUI with grouped panels and section filtering.

Description

• Add a new tui gate view in ServeCommand::renderGate() and short-circuit rendering to a new renderTui() helper when --gate=tui is selected.
• Implement renderTui(), padStrip() and stripColors() to produce a two-column TUI panel that respects --gate-sections / --gate-filter and shows portal, runtime, paths, errors and tips as requested.
• Update CLI docs (docs/CLI.md) to list tui as a valid --gate=<view> option and keep usage examples showing --gate=tui with section filters.

Testing

• No automated tests were executed for this change.

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