fix: show only direct conversation initiated by the user via the :conversation command

[tusharmath]

Summary

Add conversation tree navigation and child list views to browse parent-child conversation hierarchies, plus filter out auto-generated conversations from listings.

Context

When agents spawn child conversations (e.g., for sub-tasks), users had no way to navigate or view these related conversations. This made it difficult to track work distributed across multiple conversation threads. The conversation list was also cluttered with auto-generated conversations that users didn't initiate.

Changes

• Added new conversation-tree command (ct alias) to interactively browse child conversations spawned by the current conversation and switch between them
• Added --parent flag to select conversation to filter the conversation picker to child conversations only
• Added --parent flag to list conversation to display child conversations in structured (porcelain) format
• Filtered out auto-generated conversations from list and show views, showing only user-initiated conversations by default
• Fixed cancelled todo status icon display
• Added shell plugin support for conversation-tree action via :conversation-tree alias

Key Implementation Details

• user_initiated_conversations() filters conversations to only those where initiator == "user" and excludes conversations that are related_conversation_ids of other conversations (intermediate nodes)
• The conversation-tree command validates the parent exists, fetches children, presents an interactive selector, and switches the active conversation on selection
• list conversation --parent <id> outputs child conversations in a structured table with title and relative time ago

Use Cases

• Navigate conversation hierarchies after an agent spawns child tasks
• Quickly switch between related conversations in a tree
• Get a clean, user-initiated-only conversation list without auto-generated noise
• Shell users can use :conversation-tree to browse child conversations inline

Testing

# Build and run
cargo build

# List user-initiated conversations (filtered)
forge list conversation

# Show child conversations of current conversation
forge list conversation --parent <conversation-id>

# Interactively browse and switch child conversations
forge conversation-tree
# or
forge ct

# Via shell plugin
:conversation-tree

Links

• Related issues: N/A