Plugin TUI: Core bridge + renderer (Phases 1-2)

[hegner123]

Coroutine Bridge + Primitive Renderer

Implements the foundational coroutine bridge and rendering layer for plugin UIs. Replaces the old PTY approach (issues #98-#101, now closed) with in-process Lua coroutine yield/resume.

Plan: ai/plans/plugin/PLUGIN_TUI_SCREENS.md — Phases 1 + 2

Phase 1: Core Bridge (internal/plugin/ui_bridge.go, ui_primitives.go)

• CoroutineBridge — Create, Start, Resume, Close lifecycle
• Layout table parser — Lua table → PluginLayout / PluginPrimitive with validation
• Event builder — Go values → Lua event table
• Action parser — Lua action table → PluginAction struct
• Enable coroutine library when plugin has screens or interfaces
• Unit tests with mock Lua functions

Phase 2: Renderer (internal/plugin/ui_renderer.go)

• Each primitive type's Render(width, height, focused, accent) method
• PluginLayout → Grid + []CellContent conversion
• Single primitive rendering for inline mode
• Snapshot tests for each primitive

Primitives

list, detail, text, table, input, select, tree — all defined as Lua table shapes, parsed and rendered by Go.