feat(panel): add Insert as FX — ReaSampler 9000 onto the selected track, preloaded with the focused capture, over the existing instrument-drop body

src/core/ui/CLAUDE.md

@@ -104,6 +104,7 @@ L7 sub-pass, 2026-07-27):
 - `footer_bar` — pure footer layout/hit-test: `[Arrange|Design]` mode-toggle geometry, Tail button, and Prune placement, plus `modeSegmentEnabled` — the mode segment's live/dead predicate under the playback gate AND under whether the shell resolved a routable command id for it (both bools passed IN, so this stays REAPER-free).
 - `overflow_menu` — pure overflow-menu-button geometry/reserve/hit-test for the top-toolbar More (⋯) button.
 - `mode_enable` — pure opposite-mode enablement predicate: given the active mode, computes per-button live/disabled state for the four Item/Track × Arrange/Design tag buttons.
+- `insert_fx_enable` — pure refusal fold behind the Insert-as-FX verb (one instance holds one capture, so it needs exactly one focused capture AND a destination track), plus the button's live/dead bit derived from that same fold and one sentence per refusal. The payload/destination axes are ordered deliberately because they are knowable at different times — the header states which half the button may speak for.
 - `tooltip` — pure tooltip placement + prefix-strip: strips the `ReaSampler:` display prefix from the registered action phrase; width clamped to the client rect.
 - `card_drag` — pure drag-gesture precedence + slot hit-test: leave-client → OS drag-out; other-bank → move/copy; same-bank → reorder / Alt-over-occupied → replace.
 - `card_meta` — pure card-metadata formatters: bars.beats.subdivisions and seconds.milliseconds; blank when the sample is unstamped. Also `cardNameStrip` + the two strip constants — the card's name line sits across the TOP of the cell, drawn over the waveform exactly as the length read-out is over it at the bottom, and is suppressed entirely on a cell with no room for both strips plus a waveform band.