feat: Navbar Open-in-App Button

[sahil-noon]

Meta

Change ID	Type	Confidence	Plan	Review
6d0f	feat	3.7/5.0	13/13 tasks, 21/21 acceptance ✓	✓ 1 cycle

Impact	+/−	Net
raw	+2861 / −13	+2848
true	+2365 / −7	+2358
└ impl	+1376 / −7	+1369
└ tests	+989 / −0	+989

_{excludes fab/, docs/ · generated by fab-kit v2.16.5}

Pipeline: intake ✓ → apply ✓ → review ✓ → hydrate ✓ → ship → review-pr

Summary

run-kit surfaces sessions, panes, and worktrees, but jumping from a pane to that folder in an editor today means leaving the dashboard, finding a terminal, and running wt open by hand — worse when the browser is remote, where there is no path at all from "looking at a pane" to "that folder open in my local editor." This adds a navbar Open button: server-side exec via wt open when local, client-side ssh-remote deeplinks (VS Code/Cursor/Windsurf) when remote.

Changes

• Backend: GET /api/open-apps — new read endpoint wrapping wt open --list --json for the host-detected app registry; fail-silent (wt absent/old/erroring → 200 []).
• Backend: POST /api/open — new mutating endpoint (POST per constitution IX) launching an app on the host via wt open <path> -a <app>; validates path against a derived pane cwd/worktree path and app against the current registry before exec.
• Config: RK_SSH_HOST — new optional env var (the SSH host alias remote clients use to reach this host); unset hides the deeplink section entirely.
• Frontend: Open split-button — Conductor-style split-button in the top bar (Terminal route, v1), with a static deeplink template table for the remote case and the host dropdown for the local case; primary click re-runs the last-used target (localStorage), chevron opens the full menu.
• Frontend: command palette + keyboard — every new action keyboard-reachable via palette entries per available target.