feat(portal): render ask_user prompts on mobile chat

[agent-farnsworth]

Closes #1491

Changes

Mobile chat had no ask_user render path — a mobile user blocked on an ask_user prompt saw nothing (the shared prompt was rendered only by desktop ChatPanel.razor). This adds the mobile render + submit path.

• Move AskUserPrompt.razor into the shared BlazorClient.Core project (Components/AskUserPrompt.razor). Both Core and the desktop project share the same RootNamespace (BotNexus.Extensions.Channels.SignalR.BlazorClient), so the component keeps its exact namespace ...Components — desktop ChatPanel.razor and the desktop bUnit tests are unchanged and still resolve it via their existing @using ...Components. The component was genuinely desktop-only before (mobile references only Core), which is why it could not be reused as-is.
• Add a _Imports.razor to Core with the standard Blazor component usings (Microsoft.AspNetCore.Components.Web, etc.). Core had none, so the moved component's @onchange event binding would not compile there without it.
• Render the shared component on mobile Pages/Chat.razor as a bottom-sheet above the input bar (ask-user-sheet) whenever the active conversation has a pending prompt (Store.GetPendingAskUser). Responses route through the same IAgentInteractionService.RespondToAskUserAsync interaction the desktop uses — the submit/timeout/summary handlers mirror desktop ChatPanel exactly, so behaviour is identical across surfaces.
• Mobile bottom-sheet styles in wwwroot/css/mobile.css matching the mobile dark theme.

Tests

• New MobileAskUserPromptTests (bUnit, 7 tests): renders when a pending prompt exists; does not render otherwise (normal input remains); single-choice renders radios; multiple-choice renders checkboxes; free-form submit routes through RespondToAskUserAsync + clears the prompt; cancel routes a cancelled submission.
• Existing desktop AskUserPromptTests (IRenderedComponent<AskUserPrompt>) and all 606 desktop client tests stay green with the component in its new Core home.
• test-impacted.ps1: All impacted tests passed (Architecture + Scenarios safety nets + Mobile.Tests 63/63 + BlazorClient.Tests 606/606 + Gateway / Gateway.Conversations).

Acceptance criteria (#1491)

• Mobile renders the AskUserPrompt when a conversation has a pending ask_user.
• Mobile submit routes through the shared RespondToAskUserAsync interaction.
• Free-form, single-choice, and multi-choice prompts all render and submit.

Merge Notes

File-disjoint from the other open PRs (#1563/#1567/#1568/#1569/#1570/#1571 are all gateway/memory/cron/tools — none touch the Blazor clients), so this can merge in any order relative to them. The blocker named in the issue (#1480 mobile Chat.razor ordering) is already merged, and no open PR touches mobile Chat.razor. Part of the #1482 ask_user durability epic, but this step is independent of the Step 5 (#1487) resolution-model decision — it only renders/submits whatever pending prompt the client store already holds.

[agent-farnsworth]

CI Health Check -- PR #1572

Check	Status
impacted-tests	pass
CodeQL	pass
Analyze (csharp)	pass
Code Pattern Checks	pass
Dependency Security Audit	pass
Secret Scanning (TruffleHog)	pass

Branch: feat/askuser-mobile-render | Behind main: 0 commits | Mergeable: MERGEABLE

Actions taken:

• RESOLVED: re-triggered impacted-tests passed -- all checks now green, mergeState=CLEAN.
• The earlier impacted-tests failure was a flaky CI-timing race on 2 DESKTOP cron-sidebar tests (ConversationGroupingTests), confirmed by: full BlazorClient.Tests passing 606/606 locally on the synced commit, the test passing on main, and the single CI re-run passing green. Not a regression in this ask_user mobile PR.
• Synced main into branch (was behindBy=6); merge CLEAN, behindBy=0.

Blockers for Jon:

• None -- PR is green and CLEAN, ready for merge.

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• 2026-06-23 11:20 UTC
• 2026-06-23 11:15 UTC
• 2026-06-23 11:07 UTC

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Farnsworth (automated CI monitor) -- BotNexus -- Last updated: 2026-06-23 11:20 UTC