Smarter AI agents, duplicate stage name protection, and several interview plan fixes

Improved

• Stala handles rejections and bookings more smoothly When you give a rejection reason that matches one of your organisation's reasons, Stala uses it straight away and shows it on the confirmation card — no follow-up question. Booking a candidate into a stage they haven't reached yet now shows a single card covering both the stage move and the booking.
• Atlas asks about salary when a job description has none If a job description doesn't include a salary, Atlas now asks you right away — with suggested ranges, a "This is an unpaid role" option, and a "Decide later" option — so you're never left with a blank field.
• AI error messages are cleaner and translated Error messages from AI assistants no longer surface internal names or tool instructions. They're now translated into English and Spanish so they're always readable.
• Duplicate stage names are now blocked before you save If you give two stages in an interview plan the same name, the field flags it immediately and the plan won't save until you rename one. Blank stage names are also blocked — the field now says Required instead of showing a misleading character-count error.
• Interview stage reordering is back Drag handles are back on each custom stage in the interview plan editor so you can reorder them by dragging or with Alt + arrow keys. Built-in stages stay fixed, and custom stages can only sit between Prescreen and Offer.