feat: collapsible, reorderable categories with draggable actions

[PalmarHealer]

Summary

Three requested enhancements to the categories view (sliders & buttons):

1. Collapsible categories — a chevron per card collapses/expands it; the state is persisted in the profile.
2. Reorderable category cards — drag the ⠿ grip on a card header to reorder (cosmetic, but saved via list order).
3. Draggable actions — drag the ⠿ grip on an action row to reorder within a category, or move it to another category of the same kind (drop onto a collapsed/empty card appends).

What changed

• model: collapsed flag added to SliderCategory/ButtonCategory (serde default, so existing profiles load fine). Card order is the Vec order, so reordering persists automatically; assignments key off id, not position, so reordering is purely cosmetic.
• glue: handlers for toggle-category-collapse, reorder-category (move a card to an insertion index), and move-line (relocate an action/stream within or between categories), each with the index-shift math, then persist + re-push.
• UI (Slint): collapse chevron; ⠿ grip handles drive a hand-rolled drag-and-drop (Slint 1.16 has no native DnD). Drop targets are hit-tested from the global pointer vs each element's absolute-position, shown with an accent drop-line and a dimmed source row/card.

Implementation note

absolute-position reads are ternary-guarded so they only execute during an active drag. Reading absolute-position in a binding evaluated at init recurses through text layout (Recursion detected panic) — and Slint's && does not short-circuit the operand away, so the guard must be a ? :, not &&.

Known limitations (hand-rolled DnD)

• No auto-scroll near list edges while dragging.
• No floating drag "ghost" — feedback is the dimmed source + the accent drop-line.
• Dropping on an expanded card's header area (above the first row) may not register a slot; aim for an actual row.

Testing

• cargo build clean; cargo test passes.
• Manually verified on Windows: collapse persists across restart; cards and actions reorder; actions move between categories.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds collapsible/reorderable category cards and draggable action/stream rows to the categories view. State is persisted in the profile via a new collapsed flag and the existing Vec order. Hand-rolled drag-and-drop is implemented in Slint using absolute-position hit-testing guarded by ternaries to avoid recursion during initial layout.

Changes:

• Adds collapsed: bool (serde default) to SliderCategory/ButtonCategory and propagates it through CategorySummary to the UI.
• Adds three new callbacks (toggle-category-collapse, reorder-category, move-line) with Rust handlers (reorder_by_id, move_line) that handle index-shift math and persist the preset.
• Rewrites the category card layout to include a chevron toggle, drag grips for cards and rows, drop-mark indicators, and ternary-guarded absolute-position reads.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/model.rs	Adds collapsed field to both category structs and updates a test constructor.
src/main.rs	Updates seed CategorySummary literals with collapsed: false.
src/glue.rs	Wires three new callbacks; adds reorder_by_id and move_line helpers; includes collapsed in pushed summaries.
ui/app.slint	Adds collapsed to CategorySummary, introduces DropMark, drag state, grips, hit-test logic, and forwards new callbacks.

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