docs: describe the derived cap and cite the coupling beads (improvise-felo.1)

Review of #307 at 7b9e868b: the duplicate-step evidence and argument still
said 12, tui.md bounded a collision tuple by twelve, and the coupling
inventory named no beads. The page-bar entry now notes its unclipped
set_string can overwrite the right border.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

context/code/formula-and-io.md

@@ -736,14 +736,16 @@ is already a category. `suggested_duplicate_category` lives on the pipeline, so
 the CLI's `separate` uses the same rule.
 
 **At the category cap, Separate is shown and disabled.** The reported import
-already had 12 regular categories, which is `MAX_CATEGORIES`. Option (b) adds a
+had 12 regular categories, which was `MAX_CATEGORIES` when this was written.
+Option (b) adds a
 **regular** category, and the user declined a hidden virtual one. So at the cap
 the option is drawn "(unavailable)" with its reason and remedy: go back and
 Skip a column or make it a Measure, or choose Sum. The reason is decided in
 `ImportWizard::duplicate_options`, so every front end words it the same way.
-This is the conservative reading, and it is **an open question for the user**:
-lifting the cap for this one category, or counting it outside the cap, is a
-model-layer decision this ticket did not take.
+This was the conservative reading, and it left an open question for the user.
+**The user answered it on 2026-09-25 by raising the cap to 24**
+(improvise-felo.1), so "keep separate" is available for the reported import
+now. The option is still disabled for any import that fills the new cap.
 
 **Headless paths refuse by default.** `improvise import --no-wizard` has
 nobody to ask, so `--on-duplicate refuse|sum|separate` defaults to `refuse`.