show a tooltip on click, and keep it up until the pointer leaves

One tooltip mechanism for the whole UI: a Tooltip popup plus a
TooltipTrigger event filter, replacing every setToolTip call. Qt's own
tooltip cannot do what REQ-UI-TOOLTIP-TRIGGER and REQ-UI-TOOLTIP-DISMISS
ask for -- it times out, hides on the first mouse move, cannot be hovered
and cannot be brought up by a click.

A tooltip now appears the moment an element with no click action of its
own is clicked, and it is placed with its top-left corner on the pointer,
so the pointer can move onto the tooltip and hold it open. The pointer is
polled while a tooltip is up rather than tracked through enter and leave
events, whose order depends on which widget the pointer crosses first.

The item chip's children become transparent to the mouse. They were
taking the chip's enter and leave events, so its tooltip only ever
appeared when the pointer rested on the chip's padding.

The modal header's close button loses its "Close" tooltip: a close button
in a header says that by being one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ne3mejABZoLWKLh8fgpM3x

docs/requirements.md

@@ -439,10 +439,10 @@ Any ship, module, building, or assembler recipe id that appears in no unlock gro
 
 ### Tooltips
 
-Several UI elements carry a tooltip: the header bar's building blocks stock display (REQ-UI-BLOCKS-TOOLTIP) and artifact count (REQ-UI-ARTIFACTS-TOOLTIP), the selection panel's item chips (REQ-UI-ITEM-TOOLTIP), the build button bar's building-type buttons (REQ-UI-BUILD-TOOLTIP) and Deconstruct button (REQ-UI-DECONSTRUCT-BUTTON), and the layout configuration dialog's module selection buttons (REQ-MOD-UI-MODULE-TOOLTIP). Each of those requirements defines what its tooltip says; the two requirements here define how every one of them is shown and hidden.
+Several UI elements carry a tooltip: the header bar's building blocks stock display (REQ-UI-BLOCKS-TOOLTIP) and artifact count (REQ-UI-ARTIFACTS-TOOLTIP), the selection panel's item chips (REQ-UI-ITEM-TOOLTIP), the build button bar's building-type buttons (REQ-UI-BUILD-TOOLTIP) and Deconstruct button (REQ-UI-DECONSTRUCT-BUTTON), the layout configuration dialog's module selection buttons (REQ-MOD-UI-MODULE-TOOLTIP), and the blueprint card's delete icon (REQ-UI-BLUEPRINT-DELETE). Each of those requirements defines what its tooltip says; the two requirements here define how every one of them is shown and hidden. An element not named there carries no tooltip at all: the modal header's close button (REQ-UI-MODAL-CHROME) says what it does by being a close button, and the selection dialog's option buttons describe themselves on their own faces (REQ-UI-SELECT-OPTIONS).
 
 - REQ-UI-TOOLTIP-TRIGGER: A tooltip is shown by **hovering** the element it belongs to, after the usual short hover delay. On an element that has **no click action of its own** it is in addition shown **immediately on left click**, without waiting the delay out. That covers the header bar's building blocks stock display and artifact count and the selection panel's item chips: these display a value and do nothing when clicked, so a click on them is free to mean "tell me what this is", which is quicker than waiting on a hover and is the obvious thing to try. It does not cover elements whose click already does something — the building-type buttons, the Deconstruct button, and the module selection buttons — whose tooltips are reached by hovering alone, so that one gesture never both acts and explains. Only the left mouse button shows a tooltip; the right and middle buttons never do. Clicking an element whose tooltip is already up leaves it up.
-- REQ-UI-TOOLTIP-DISMISS: A tooltip stays visible until the pointer leaves **both the tooltip and the element it belongs to**, however it was triggered. It does **not time out**: there is no display duration after which it vanishes on its own, so a tooltip listing several recipe lines (REQ-UI-ITEM-TOOLTIP) can be read at whatever pace the player needs. The tooltip is itself part of the area that keeps it open — moving the pointer off the element and onto the tooltip does not hide it — which requires the tooltip to be placed **adjacent to its element**, leaving no gap the pointer would have to cross to reach it. Once the pointer is outside both, the tooltip hides. Nothing else dismisses it, and nothing else needs to: a click elsewhere is a click the pointer has already travelled to, so the tooltip is gone before it lands.
+- REQ-UI-TOOLTIP-DISMISS: A tooltip stays visible until the pointer leaves **both the tooltip and the element it belongs to**, however it was triggered. It does **not time out**: there is no display duration after which it vanishes on its own, so a tooltip listing several recipe lines (REQ-UI-ITEM-TOOLTIP) can be read at whatever pace the player needs. The tooltip is itself part of the area that keeps it open — moving the pointer off the element and onto the tooltip does not hide it — which is what fixes where it is placed: its **top-left corner sits at the pointer**, at the position the pointer had the moment the tooltip was triggered. The pointer therefore starts on the tooltip's own corner and reaches the rest of it without crossing a gap. A tooltip that would run off the screen is pushed back onto it, which only moves it further over the pointer. Once the pointer is outside both, the tooltip hides. Nothing else dismisses it, and nothing else needs to: a click elsewhere is a click the pointer has already travelled to, so the tooltip is gone before it lands.
 
 ### Layout
 
@@ -838,7 +838,7 @@ Blueprints occupy no permanent screen space. They are saved with **Ctrl+C** from
   - After the transfer the game stays in blueprint placement mode, so further same-type buildings can be clicked in turn.
   - A blueprint placement applies every transfer among its ghosts in the same click that places its new construction sites (REQ-UI-BLUEPRINT-PLACE); the placement is all-or-nothing, so if any ghost is invalid nothing is placed and nothing is transferred.
 
-- REQ-UI-BLUEPRINT-DELETE: Clicking the delete icon ("×") on a blueprint card (REQ-UI-BLUEPRINT-CARD) immediately removes that blueprint from the list, without a confirmation prompt. The blueprint selection dialog stays open and its card grid reflows to close the gap. If the deleted blueprint was active in blueprint placement mode, that mode is exited.
+- REQ-UI-BLUEPRINT-DELETE: Clicking the delete icon ("×") on a blueprint card (REQ-UI-BLUEPRINT-CARD) immediately removes that blueprint from the list, without a confirmation prompt. The icon carries a hover tooltip naming what it does, since a bare "×" on a card could as easily mean closing something (REQ-UI-TOOLTIP-TRIGGER, REQ-UI-TOOLTIP-DISMISS). The blueprint selection dialog stays open and its card grid reflows to close the gap. If the deleted blueprint was active in blueprint placement mode, that mode is exited.
 
 - REQ-UI-BLUEPRINT-SAVE: On application shutdown, all current blueprints are serialized to a file named `blueprints.toml` located in the same directory as the application executable. The TOML structure matches REQ-UI-BLUEPRINT-STORAGE. Write errors are silently ignored on shutdown (no button, no dialog).