Fix variable-editor dialog closing when resizing the editor

[nabramovitz]

Closes #5486

Problem

The app variable editor (Applications → Variables → Add/Edit) put a CSS resize grip on a small box hugging the Monaco editor. Dragging it to enlarge released the pointer on the backdrop, and the browser's synthesized click resolved to the overlay — which the dialog read as a backdrop click and closed. The editor "resized, then vanished."

Changes

Backdrop dismissal hardened (tailwind-dialog.service.ts) — closing now requires the press to have started on the backdrop, not just the release. A drag that begins inside a dialog (resize grip, text selection) and ends on the backdrop no longer dismisses it. This was latent for every dialog.

Dialog is now movable + corner-resizable instead of the inner editor box. Opt-in draggable/resizable config flags:

• pin the panel to a fixed viewport position so the native resize grip tracks the cursor 1:1 (a flex-centered panel re-centers and drifts);
• let it be dragged by its header (data-dialog-drag-handle);
• make the Monaco editor flex-fill the panel so it grows/shrinks with it (automaticLayout re-fits);
• clamp both drag and resize to the viewport, so the panel and its action buttons can never be pushed off-screen.

Verification

• Unit: dialog service spec covers backdrop-drag-doesn't-close, genuine backdrop click still closes, resizable/draggable setup, viewport clamp on drag and resize. All green.
• Production build (ng build stratos --configuration production) clean.
• Live against a real CF app: editor grows with the panel; header drag moves it; drag-release on backdrop keeps it open; genuine backdrop click dismisses; drag and resize both clamp on-screen.

Known minor edge

The viewport clamp is computed at open and after each move, not on browser-window resize while the dialog is open. Shrinking the OS window mid-edit could overflow until the panel is nudged — rare for a transient editor; can add a resize re-clamp if wanted.

[norman-abramovitz]

LGTM