Follow-up: provision cancellation UX polish

Tracking issue for follow-up work on the Ctrl+C provision cancellation flow introduced in #7795. These items came out of @kristenwomack's customer-experience review and were intentionally deferred from that PR to keep its scope focused on the customer-blocking copy/telemetry fixes (R1, R2, R3, R4, R9, R10, R11, R15, R16, all shipped in 9071f57e).

## Should-improve

- [ ] **(R5) Option ordering / labels.** Pressing Ctrl+C signals "stop" — listing 'Leave the Azure deployment running and stop azd' first makes users re-read. Consider listing 'Cancel the Azure deployment too' first while keeping 'Stop azd, but let Azure finish the deployment (default)' as the highlighted default. Needs a quick check that our \`Select\` widget supports default-selection independent of display order.
- [ ] **(R6) 5-minute wait UX.** Today the user just stares at a single spinner for up to 5 minutes during the cancel-await window. Add: (a) elapsed-time tick on the spinner (\`Waiting for Azure to confirm cancellation… 45s / 5m\`); (b) consider a 60–90s foreground wait that auto-degrades to a \`still canceling, track here\` message + background exit; (c) a third Ctrl+C (during cancel-await) that abandons the *wait* (not the cancel) and prints the portal URL.
- [ ] **(R7) Discoverability of new Ctrl+C semantics.** Users have no way to learn the new behavior. Add a session-level tip on \`azd provision\` / \`azd up\` startup, an \`aka.ms/azd/ctrlc\` link in prompt help, and consider an \`AZD_INTERRUPT_MODE=immediate|prompt\` env var for power users who want the old default-immediate-exit behavior back.
- [ ] **(R8) Mirror docs to learn.microsoft.com.** \`cli/azd/docs/provision-cancellation.md\` is contributor-facing. Mirror to public docs and reference the public URL from the prompt help / aka.ms link.

## Nice-to-have

- [ ] **(R12) Skip the prompt for Deployment Stacks.** Stacks don't support per-deployment Cancel; today we surface that as a \`leave-running\` outcome *after* the user picks Cancel. Detect provider shape up front and go straight to leave-running with explicit messaging instead of offering a choice that doesn't exist.
- [ ] **(R13) Spinner→prompt accessibility.** The transition from spinner to interactive prompt can be missed by screen readers (e.g. NVDA on Windows Terminal). Emit a non-overwritten plain line first (\`Interrupt received. Showing options:\`).
- [ ] **(R14) WCAG 1.4.1 color check.** Confirm that the consequences of the leave-running choice are not conveyed by color alone — pair the warning color with \`⚠\` or \`[warning]\` text.

Each item is small enough to ship independently.

cc @kristenwomack @vhvb1989