feat(hub-ui): clone project — create new project from existing project settings

## Problem

When setting up a new project that should have similar configuration to an existing one (templates, agent configs, env vars, shared directories), there's no way to clone or copy settings. Users must manually recreate everything from scratch.

## Proposed Solution

Add a "Clone Project" action in the Hub UI that:
1. Creates a new project with a user-specified name/slug
2. Copies templates, agent template assignments, and configuration from the source project
3. Does NOT copy secrets, active agents, or session state (clean start)

## Scope

- Limited to **new project creation** only — not modifying existing projects
- UI-initiated (not an agent action)
- Source project must be accessible to the user
- Cloned project starts empty (no running agents) but with the same template and config foundation

## UX

In the Hub UI project list or project settings:
- "Clone Project" button → dialog with new project name → creates clone
- Or: "New Project" flow with an optional "Start from existing project" dropdown

## Security

Minimal concern — this is equivalent to a user manually creating a new project and configuring it the same way. No cross-tenant access, no secret leaking (secrets are not copied).

Start by locating the Hub UI project-creation flow and the project configuration persistence used for templates, agent template assignments, environment variables, and shared directories. Define the clone entry point and new-project name/slug handling, then verify that secrets, active agents, and session state are excluded and that the source project remains access-controlled.

Written by the indexing model from the issue text.