Merge doubled CLI formatting stacks (output_formatters.py + rich_output.py) behind a presentation-neutral layer

[eman]

Summary

Deferred follow-up from #95 (comprehensive repo evaluation, batch 6: architecture cleanup).

The CLI currently maintains two large, largely parallel formatting stacks:

• src/nwp500/cli/output_formatters.py (~1106 lines)
• src/nwp500/cli/rich_output.py (~982 lines)

Together these total roughly 2100 lines with significant overlap in responsibility (formatting the same device/status/schedule data for different output modes), which increases the maintenance burden whenever a new field or command is added — logic has to be updated/kept-in-sync in two places.

Suggested approach

• Introduce a presentation-neutral intermediate representation (e.g. structured rows/sections) that both the plain-text and rich-based renderers consume.
• Migrate formatting logic incrementally so both stacks call into shared data-shaping code, leaving only true rendering-technology differences (colors, tables, plain strings) in each module.
• Consider whether one of the two stacks can be retired entirely if presentation differences turn out to be minor.

Acceptance criteria

• Duplicated formatting/data-shaping logic between the two modules is eliminated or minimized.
• CLI output (both plain and rich modes) is unchanged for existing commands, verified by existing CLI tests.
• ruff/mypy clean.