Introduce QuickActionsService and QuickAgent for lightweight, single-shot AI
operations. Add a dedicated quickActionModel setting alongside a new top-level
provider setting, with validation ensuring all models match the selected provider
and provider-specific defaults. Refactor FileSystemService to offer both TFile
and path-based overloads (readFile/readFilePath, writeToFile/writeToFilePath,
patchFile/patchFileAtPath). Replace window/document globals with activeWindow/
activeDocument throughout InputService and VaultkeeperAISettingTab for Obsidian
mobile compatibility.
Update linting packages to latest.
