fix: store hook_event, tool_use_id, and tool_input as indexed columns instead of JSON blobs

[tumberger]

Problem

Several high-value fields are buried inside request_json JSON blobs in the mcp_events table instead of being stored as first-class indexed columns:

Field	Current storage	Impact
hook_event	Inside request_json.hookEvent	Cannot efficiently query "all PreToolUse events" without JSON path scan
tool_use_id	Inside request_json.toolUseId	Cannot efficiently correlate Pre/Post events without JSON extraction
tool_input	Inside request_json.toolInput	Cannot index or filter by input properties

Meanwhile tool_name and response_json are already proper columns.

Fix

This is an API/DB concern, not a CLI concern. The API handler should extract these fields from the proto message and store them in dedicated columns:

1. Add hook_event column to mcp_events (or use the existing event_type column more precisely)
2. Add tool_use_id column to mcp_events
3. Consider promoting tool_input to its own JSON column (parallel to response_json)

Requires a DB migration.

Note

This issue is tracked here for visibility but the fix lives in the API repo, not the CLI.