Split the TUI god-files and gate repaints on change

[TheGreatAxios]

Summary

• Splits the three TUI god-files into layered single-concern modules: shell (12 modules), provider (11), runner (11); the 6,139-line shell file is gone and the largest remaining TUI module is 1,470 lines
• Deletes hand-rolled code OpenTUI already ships: the list viewport and selection math (SelectRenderable), clipboard helper discovery and OSC 52 writing, overlay fixture fallbacks, and the dead tui barrel
• Coalesces stream and tool row updates to one retext per renderer frame with flush-on-close seams, recomposes chrome only when its composed inputs change, and skips unchanged tool elapsed ticks
• Adds a CI-enforced per-file line-budget ratchet, layered import-direction rules, and an import-graph test so the tree cannot silently re-tangle or regrow
• Fixes the clipboard-failure crash, overlay selection reset on resize, and mid-sentence decision clipping found during review, each pinned by a regression test

Verification

• bun run check passes with 6,288 tests and 0 failures, verified in two independent full-suite runs
• bun run tui:smoke passes
• Perf gates: N deltas in one frame produce one retext; ten idle stickyPoll ticks produce zero chrome recomposes; shape-stable row updates produce zero subtree rebuilds

Fixes CL-6791

[linear-code]

CL-6791