Enhance Pair Writing Mode: Add Discuss action and streamline UX

[rjroy]

Summary

• Added "Discuss" advisory action for open-ended conversation about selected text
• Streamlined Quick Action UX by removing toast notifications
• Refactored prompt building to reduce code duplication and improve maintainability
• Updated snapshot button styling for better visual distinction

Changes

New Feature: Discuss Action

Added a new advisory action type that enables freeform discussion about selected text:

• Backend prompt configuration with role and instructions
• Frontend context menu integration with message bubble icon
• Consistent with existing advisory actions (Validate, Critique, Compare)

UX Improvements

Removed Toast notifications from Quick Actions:

• Quick Action confirmations previously showed in toast notifications
• Now Quick Actions appear directly in the conversation pane via onQuickAction prop
• Cleaner integration with the shared discussion context
• Simplified PairWritingEditor component (removed Toast dependency)

Snapshot button visual polish:

• Changed color from accent to success green (--color-text-success)
• More intuitive indication that snapshot exists

Code Quality

Refactored prompt building:

• Consolidated Validate/Critique/Discuss prompts using buildStandardAdvisoryPrompt
• Extracted shared formatting logic (formatRules)
• Compare action retains unique structure (before/after comparison)
• Maintains backward compatibility with exported individual builders

Simplified PairWritingEditor:

• Removed toast state management and chunk accumulation logic
• Streamlined response handling with switch statement
• Cleaner dependency injection (removed ToastComponent prop)
• Reduced component complexity by 150+ lines

Test Plan

• All existing tests pass (./git-hooks/pre-commit.sh)
• Type checking passes across all workspaces
• Linting passes across all workspaces
• Discuss action appears in context menu
• Discuss action sends proper advisory action request
• Quick Actions no longer show toast notifications
• Quick Actions appear in conversation history
• Snapshot button displays with green success color
• All four advisory actions (Validate, Critique, Compare, Discuss) work correctly

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 94.28571% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
backend/src/pair-writing-prompts.ts	89.83%	6 Missing ⚠️
frontend/src/components/PairWritingEditor.tsx	97.22%	1 Missing ⚠️
frontend/src/components/PairWritingMode.tsx	95.65%	1 Missing ⚠️

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