End a held bubble's hover on release, and let physics mode follow graph changes

[sorenwacker]

Two changes to bubble mode, one commit pair (change with tests, then docs) each.

• Fixes A bubble stays hovered, with its edges highlighted, after the pointer is released over the preview panel #130: a pressed bubble stayed hovered, its edges thick and highlighted, when the pointer was released over the preview panel, which stops pointerup. The bubble canvas now listens for the release in the capture phase. The new test fails on the unfixed code.
• Closes Physics mode should take in nodes and edges added while it runs #131: while physics mode is on, a node or edge added or removed (by an MCP client, the agent or the user) is taken into the simulation: positions reached so far are stored, the simulation is rebuilt on the graph as it now is, and it reheats, without another undo step. Creating or deleting a node used to end the mode and discard the simulated positions. A change that only moves nodes still ends the mode.

Not tried in the running app. Full suite: 1507 tests.