v0.15.2

fix(v0.15.2): in-app prompt dialog + electron.log resets per launch

Two small fixes.

Session rename from the dashboard didn't work because Electron's
Chromium renderer disables window.prompt() entirely. Added an
appPrompt() helper alongside appConfirm() in src/confirm.tsx — same
custom-modal pattern, with an input field, autofocus + select, Enter
to submit, Esc/click-outside to cancel. Dashboard's rename + delete
both go through these now.

Also: electron.log was opened in append mode, so every relaunch
accumulated against the previous session's log. Truncate the file on
process start so the log file always represents the current run only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>