fix(workbench): Positron git-ops readback times out (console proven in isolation)

The Positron console readback mechanism is proven in isolation: a probe wrote a file via the terminal and read it back through the console (.console-instance[style*="z-index: auto"] / .console-input / div span, after the interpreter is input-ready) — PASS. But the git-ops clone_positron/push_positron flow times out:

ExecError: terminal_run timed out after 840000ms waiting for done marker in '/tmp/vip_term_*.txt'

The DONE marker never appears in the temp file within the poll window.

Likely causes to investigate (live, ~20 min/iteration)

• The git clone may not actually execute in Positron's terminal (so the temp file / DONE marker is never written).
• The poll loop's repeated Console-tab activation + re-typing of cat(readLines(...)) may interfere with the running terminal command.
• The clone may fail (auth/token/path), so && echo DONE short-circuits and DONE is never appended.

Launch gate

launch_positron currently gates on .positron-console being visible, which spuriously SKIPS whenever the Terminal tab is active (Positron loaded, console hidden). A Console-tab gate (PositronSession.CONSOLE_TAB = 'a.action-label[aria-label="Console"]') is more correct, but it exposes the readback timeout above (turns a graceful skip into a failure). Reintroduce the Console-tab gate together with the integration fix.

Context

• Sibling fix #386 reworked the readback: RStudio (R console), Positron (console eval — proven here in isolation), VS Code (editor-open — validated end-to-end in git-ops).
• positron_eval_r/positron_eval_python already activate the Console tab (exec._activate_positron_console); the remaining gap is the end-to-end clone+readback integration.
• Related: slow Positron session/console cold-start (#388).

Start with launch_positron, clone_positron, and push_positron, then trace positron_eval_r/positron_eval_python and exec._activate_positron_console. Reproduce the timeout while checking terminal execution, the DONE marker, and repeated Console-tab activation. Done means the Console-tab gate is restored and the end-to-end Positron clone and push readback completes without timing out.