feat: add ratatui TUI backend with nemo-ui/nemo-tui crate split

[geoffjay]

Summary

• Extract GPUI code into nemo-ui crate: Moves all GPUI-specific code (54 components, workspace, theme, config, runtime, window) from the nemo binary into a dedicated nemo-ui library crate with a run_gpui() entry point
• Create nemo-tui crate with ratatui rendering: New terminal UI backend that maps XML components to ratatui widgets (stack→Layout, panel→Block, label/text→Paragraph, progress→Gauge, table→Table) with graceful degradation for unsupported types
• Add --tui/--ui CLI flags: Mode detection with priority: CLI flag > <app default="tui"> XML config > default to GPUI

Architecture

XML config → nemo-config → nemo-layout → BuiltComponent tree
                                              |
                                  +-----------+-----------+
                                  |                       |
                             nemo-ui (GPUI)         nemo-tui (ratatui)
                                  |                       |
                               Desktop               Terminal

New crates

Crate	Purpose
nemo-ui	GPUI desktop rendering (extracted from nemo binary)
nemo-tui	ratatui terminal rendering (new)

TUI component mapping

XML Component	ratatui Widget
stack	Layout (horizontal/vertical with flex constraints)
panel	Block (borders + title, children inside)
label	Paragraph (single line)
text	Paragraph + Wrap (multi-line)
progress	Gauge (value/max ratio)
table	Table (column definitions + row data)

Test plan

• All existing workspace tests pass (0 failures)
• 12 new integration tests for TUI components using ratatui TestBackend
• cargo run -- --app-config examples/basic/app.xml — GPUI still works
• cargo run -- --app-config examples/tui-basic/app.xml — TUI mode via default="tui"
• cargo run -- --app-config examples/basic/app.xml --tui — Force TUI on GPUI config

🤖 Generated with Claude Code