Add .claude/settings.json with SessionStart hook running agent-brief.sh

[infraax]

Task: Session Start Hook

Parent epic: #13 (Infrastructure)
Depends on: #21 (agent-brief.sh)

What to do

Create .claude/settings.json with a SessionStart hook that runs agent-brief.sh automatically when Claude Code starts in this repo. Every agent gets context before typing a single message.

{
  "hooks": {
    "SessionStart": [
      {
        "type": "command",
        "command": "bash ./scripts/agent-brief.sh"
      }
    ]
  }
}

Why this matters

Without this, every agent session starts cold and must manually read CLAUDE.md + README + recent git log. With this, the brief runs automatically — zero token overhead for orientation, just immediate context.

Notes

• Only add the SessionStart hook — don't add other hooks that would interfere with agent work
• The hook output appears in the agent's context at session start
• If agent-brief.sh doesn't exist yet, the hook should fail gracefully (not crash Claude Code)
• Keep .claude/settings.json minimal — no settings that change agent behavior beyond the brief

Definition of done

Opening Claude Code in this repo shows the agent brief automatically in the first message context.