2.6.0 - RAG, Multilingual Support & Mass Edit

What's new:

RAG Enhancements
RAG Statistics tab in admin: 4 summary cards tracking query tokens, response times, and document matches; recent queries table (50 rows, formatted units)
Multilingual RAG: User queries auto-respond in their UI language via language hints (no schema changes required)
Localized "Ask AI" sliding panel fully translated to 20 languages
Language dropdown in test tab; optional language tagging in upload form

Grid & Bulk Operations
Mass Edit module: select rows via checkboxes → bulk edit fields, export CSV, assign owner, duplicate, or delete with confirmation
Grid keyboard shortcuts (arrow keys, Tab, Ctrl+C copy, Ctrl+F search, Help modal via Ctrl-hold) across all 20 languages
Quick Data Cleanup toolbar button (editors only): find & replace text with live preview, case sensitivity, accent-ignore options

Admin
Renamed "RAG Knowledge Base" → "Centrum AI" heading
Release Migration Manager: pending file/config cleanup tasks after version upgrades, with audit trail and automatic backups

Fixes
Fixed api_rag.php regression: restored page_context support and query logging
Fixed rag_call_ollama() return type annotation (now array instead of string)
CSV Import: fixed duplicate "Step 1" UI race condition; conflict column no longer defaults to id
Pinned qs and uuid dependencies (Dependabot security alerts)

What's Inside
All operations (mass edit, cleanup, bulk delete) are editor-role gated, CSRF-protected, and audit-logged. FK columns render as dropdowns in forms. Full i18n support (20 languages) across all new modules.