tui(M4.2): read grouping + SpillableText + open pager

[emal-avala]

Parent #390 (M4) · Epic #385

≥3 consecutive successful read-only cards group as view-only fold; SpillableText head/tail + tempfile; o suspend-exec pager.

Acceptance

Grouping unit tests; spill 5k line bash scripted test.

[emal-avala]

Triage against main @ 6eb1282 — grouping done, spill+pager not. Done: ≥3 consecutive completed read-only cards fold (MIN_GROUP=3, toolcard.rs:80, plan_display :92-116, tests :145-212; fold render layout.rs:423-450). Remaining: no SpillableText (tempfile head/tail) anywhere — the only cap is live-tail truncation (app.rs:709); no o pager binding (the suspend-exec machinery exists at run.rs:176 with_main_screen and is used for interactive slashes, so the pager is mostly wiring).