feat: fleet cli ux

[davideast]

Overhauls the @google/jules-fleet CLI with an event-driven rendering architecture, an interactive init wizard, and a conflict-resistant file structure.

Init Wizard (jules-fleet init)

• Interactive mode (TTY): Guided @clack/prompts wizard — repo detection, auth selection, secrets upload, confirmation
• Non-interactive mode (--non-interactive): All inputs via flags/env vars with actionable errors for missing values
• Dry run (--dry-run): Preview files without creating a PR
• Secrets upload: Optional upload of JULES_API_KEY and GitHub App credentials to GitHub Actions secrets via NaCl sealed-box encryption

New flags: --non-interactive, --dry-run, --auth, --app-id, --installation-id, --upload-secrets

Event-Driven Rendering

• Typed event system with per-domain event files (events/init.ts, events/merge.ts, etc.)
• FleetEmitter function replaces direct logging in all handlers
• RenderContext abstraction decouples domain logic from output format

Bug Fix: Init All-Files-Exist Guard

• jules-fleet init on an already-initialized repo now returns a clear ALREADY_INITIALIZED error with a suggestion to use configure instead, rather than failing with a cryptic GitHub API error

Architecture

shared/
├── events/
│   ├── init.ts          # 16 event types
│   ├── configure.ts     # 6 event types
│   ├── analyze.ts       # 8 event types
│   ├── dispatch.ts      # 7 event types
│   ├── merge.ts         # 18 event types
│   └── error.ts         # 1 event type
├── ui/
│   ├── spec.ts          # FleetRenderer + RenderContext interfaces
│   ├── interactive.ts   # Thin shell → delegates to render/*
│   ├── plain.ts         # Thin shell → delegates to render/*
│   └── render/
│       ├── init.ts      # Domain-specific render function
│       ├── configure.ts
│       ├── analyze.ts
│       ├── dispatch.ts
│       ├── merge.ts
│       └── error.ts
init/
├── wizard/
│   ├── types.ts         # InitWizardResult, InitArgs
│   ├── interactive.ts   # @clack/prompts wizard flow
│   ├── headless.ts      # Flag/env validation for CI/agents
│   └── index.ts         # Barrel re-exports
├── ops/
│   └── upload-secrets.ts # NaCl encryption + GitHub Secrets API