feat: send CLI version, duration, and byte counts with events

[tumberger]

Problem

Several fields that the API supports and stores are never populated by the CLI:

Field	Current state	Impact
clientVersion	Never sent, always null	No way to know which CLI version generated an event — makes debugging and compatibility tracking impossible
durationMs	Hardcoded to 0	No tool execution timing. For PostToolUse events, the time between Pre and Post is knowable but not calculated
bytesIn / bytesOut	Never computed	No payload size tracking despite having tool_input and tool_response data

Fix

CLI version

• Add CLI version to CreateSessionRequest.client_info map (e.g. {"name": "kontext-cli", "os": "darwin", "version": "0.1.0"})
• The version is already available via ldflags (-X main.version=...) from goreleaser

Duration

• For PostToolUse events: compute elapsed time since the corresponding PreToolUse event (match by tool_use_id)
• The sidecar can maintain a map of tool_use_id → start_time from PreToolUse events
• Add duration_ms to the proto or compute it server-side by correlating Pre/Post events

Byte counts

• Compute from len(tool_input) and len(tool_response) before sending
• Add bytes_in and bytes_out fields to the proto