UX: Show tech stack detection results and allow override on init

[frankbria]

Problem

When initializing a workspace with detect: true, the UI auto-detects the tech stack silently. Users don't see what was detected or have a chance to correct it. If detection fails, WorkspaceStatsCards shows 'Not detected' with no explanation or recovery path.

Impact

Users unsure if tech stack detection succeeded or if the agent will make incorrect technology assumptions during execution.

Recommendation

1. After init with auto-detect, show a confirmation dialog: "Detected: Python with uv, pytest, ruff. Is this correct?" with Confirm / Edit options
2. Display detection status in WorkspaceHeader (✓ if detected, ⚠ if missing)
3. Add 'Edit Tech Stack' link/button to WorkspaceStatsCards or WorkspaceHeader
4. On detection failure: show actionable message "Could not auto-detect. Enter your stack manually."

Acceptance Criteria

• Post-init dialog shows detected tech stack for confirmation
• User can override detection before confirming
• WorkspaceHeader shows detection status indicator
• 'Edit Tech Stack' accessible at any time post-init
• Failure state shows specific actionable recovery steps

Affected Components

web-ui/src/app/page.tsx, web-ui/src/components/workspace/WorkspaceHeader.tsx, web-ui/src/components/workspace/WorkspaceStatsCards.tsx

[traycerai]

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