Restrict lead status changes by role and ownership

[mprinceb]

Motivation

• Prevent unauthorized users from changing a lead's top-right status in the UI while allowing owners and higher roles to edit it.
• Ensure programmatic attempts to change status are blocked if the user lacks permission.

Description

• Added a canChangeLeadStatus computed property to frontend/src/pages/Lead.vue that returns true for Admin/System Manager, Sales Manager and Sales Master Manager, or for a Sales User when doc.owner === session.user.
• Updated the status control to render the editable Dropdown only when canChangeLeadStatus is true and render a read-only Button showing the status otherwise.
• Added a guard in triggerStatusChange to display an error toast and abort when canChangeLeadStatus is false.
• All changes are contained in frontend/src/pages/Lead.vue.

Testing

• Ran yarn build which failed in this environment due to missing local Frappe files (sites/common_site_config.json and frappe/frappe/public/js/lib/posthog.js).
• Started the dev server with cd frontend && yarn dev to validate UI changes; the server started but runtime import resolution errors for the same missing local files were observed in this environment.
• Captured a browser screenshot of the running app shell via an automated Playwright script to visually validate the lead page rendering, which produced an artifact successfully.

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Codex Task