Show user prompt separately from orchestration wrapper in chat UI

[StephaneDelcroix]

Problem

When using multi-agent orchestration (broadcast, sequential, orchestrator modes), the user's prompt gets wrapped in a larger context prompt that includes multi-agent context prefixes, orchestrator planning instructions, worker task assignments, etc. The full wrapped prompt was shown in the chat UI, making it hard to read and overwhelming.

Fix

• Added OriginalContent property to ChatMessage to store the user's original typed text when Content contains the full orchestration-wrapped version
• Threaded originalPrompt parameter through SendPromptAsync and SendPromptAndWaitAsync so orchestration callers can provide the user's original text
• Updated all orchestration send paths (broadcast, sequential, orchestrator planning, worker dispatch, synthesis, reflect cycle) to pass the original prompt
• Updated ChatMessageItem.razor to display OriginalContent as the visible message, with a collapsible <details> element showing the full orchestration prompt
• Added CSS styling for the collapsed prompt section

What it looks like

• User sees their original prompt text prominently in the chat
• A "Full orchestration prompt" disclosure triangle lets them expand/collapse the wrapped version
• When OriginalContent is null (regular non-orchestrated messages), behavior is unchanged

Testing

• 8 new unit tests in OrchestrationPromptDisplayTests.cs covering OriginalContent behavior
• 5 additional tests in ChatMessageTests.cs for the new property
• All 1557 existing tests pass (1 pre-existing locale failure unrelated to this change)

[PureWeen]

If you've ran these through pr multi squad of power until it says it's mergeable just merge em

[StephaneDelcroix]

✅ Multi-Model Review: Ready to Merge

Two fixes applied during review:

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Fix 1 — OriginalContent not persisted (commit 538f8d4)

Previous finding (3/5 models): OriginalContent on ChatMessage was not mapped in ChatMessageEntity, so it was silently dropped on app restart.

Fixed: Added OriginalContent column to ChatMessageEntity and mapped it in both ToChatMessage() and FromChatMessage(). sqlite-net-pcl auto-migrates the nullable column; existing rows get null (pre-PR behavior).

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Fix 2 — MonitorAndSynthesizeAsync resume path missing originalPrompt (commit 6d00df5)

Found during re-review (2/5 models): CopilotService.Organization.cs:1363 — SendPromptAsync in the orchestration resume path (MonitorAndSynthesizeAsync) called without originalPrompt: pending.OriginalPrompt, so the synthesis message after app restart would show the full wrapped prompt instead of the user's original text. All other orchestration call sites were correctly updated.

Fixed: One-line change to pass originalPrompt: pending.OriginalPrompt at that call site.

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All 1557 tests pass (1 pre-existing locale-dependent failure unrelated to this PR).

Post-fix re-review (5 models): No further issues found. ✅