fix: forward Claude Code session_id and permission_mode to backend

[tumberger]

Problem

Two fields from Claude Code's hook stdin JSON are parsed but dropped before reaching the backend:

1. Claude Code's native session_id

• Parsed by the claude adapter in DecodeHookInput
• Stored in agent.HookEvent.SessionID
• Dropped in main.go's evaluateViaSidecar() — the EvaluateRequest struct has no SessionID field
• The Kontext session ID is used instead, so Claude Code's own session identity is lost

2. permission_mode

• Parsed by the claude adapter's hookInput struct
• Dropped at the adapter layer — never transferred to agent.HookEvent
• This field indicates whether Claude Code is running in default, plan, or bypassPermissions mode — important security context

Impact

• Cannot correlate Kontext events back to a specific Claude Code session (matters when multiple Claude instances share a Kontext session)
• No visibility into whether the agent was running with permissions bypassed — critical for audit/compliance

Fix

1. Add SessionID and PermissionMode fields to sidecar.EvaluateRequest
2. Add corresponding fields to the proto ProcessHookEventRequest
3. Store both in the events table