feat(desktop): /journey opens the memory graph overlay instead of printing text

[OutThisLife]

Summary

• /journey (and its aliases /learning, /memory-graph) in the desktop app used to fall through to slash.exec and dump the CLI's text timeline into the transcript. It now opens the desktop's memory graph overlay (the starmap at /starmap) — the same surface the command palette's "Memory Graph" entry opens, and the desktop counterpart of the TUI's /journey overlay (ui-tui/src/app/slash/commands/ops.ts).
• Wiring follows the registry pattern: a new journey DesktopActionId row in desktop-slash-commands.ts plus an actionHandlers entry in use-prompt-actions/slash.ts that calls an injected openMemoryGraph(). desktop-controller.tsx supplies openStarmap from useOverlayRouting(). Args are ignored, matching the TUI overlay behavior.
• /journey now also appears in the slash popover/completions (it previously surfaced only as an unfiltered extension row with the CLI description).
• The second commit fixes two pre-existing perfectionist import-order lint errors in use-prompt-actions/index.ts + submit.ts (present on main before this branch).

Test plan

• vitest run --environment jsdom src/lib/desktop-slash-commands.test.ts src/app/session/hooks/use-prompt-actions/index.test.tsx — 53 passed, including new coverage: /journey + aliases resolve to the journey action, and the dispatcher opens the overlay without hitting slash.exec / command.dispatch
• tsc -p . --noEmit clean
• eslint clean on all touched files