Terminal: a right-click menu that fits, Backspace deletes a selection (#44)

[Maxaubert]

Closes #44. Owner, 2026-09-23.

The right-click menu fits what was clicked (this app's menu):

• Over a link: Copy link first, the whole link even across a wrap.
• With text marked: Copy, exactly the selection.
• Then Paste, Find in scrollback, Command help. Close tab is gone from this menu; the tab's own menu, Ctrl+W and the X keep it.
• Copies go through main's clipboard (writeClipboard), like command help.

Backspace deletes a selection (in core/, so this is a change to Prism's terminals too):

• Backspace or Delete, unmodified, over a selection that starts and ends on the line being edited sends Left/Right to the selection's end, then one DEL per character.
• The click-to-place-caret refusals apply (a program owning the mouse, full screen, scrolled back, hidden cursor, text below); anywhere else the key is the shell's, untouched.
• Pure rules in core/renderer/lib/termSelectionEdit.ts; termContextAt (core, read-only) answers what is under a point, which Prism's menu can use after the bump.

Versions: app 0.12.0 -> 0.13.0, core 0.10.0 -> 0.11.0.

Tests

• Unit: termSelectionEdit.test.ts (gate, end/middle/backwards selections, trailing cells, wide characters, application cursor keys, linkAt). 882 passed; typecheck; lint 0 errors.
• e2e selectionEdit, real pwsh, real drag and keys: Backspace over a selected word at the end, and in the middle; a selection in old output leaves Backspace to the shell; right-click on a link shows Copy link first and copies it (read back in main); plain text offers no Copy; marked text offers Copy and copies it exactly; no Close tab. Fails on the old code. dropAndMenu now asserts Close tab is absent.
• Full e2e: all scenarios passed except spawn once ("an empty launch lands on the start screen"), as the first scenario right after a hung earlier run's processes were killed; it passes on a rerun, on this branch and on main.

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