feat: rebrand QuestboardAI -> TaskFlow everywhere (UI, locales, index.html)

Implement paywall modal, subscription pages, and translation keys

feat: rebrand PlotTwist to QuestboardAI

feat: rebrand TaskFlow to PlotTwist and align with Human-in-the-Loop AI Agent Proof-of-Work vision

feat: integrate sketchy brain logo branding and add workspace agent guidelines

init