fix: add type field to image attachments, fix attachment cap message wording

feat: send PDF attachments as document content blocks to Claude API

feat: render PDF attachment cards with doc icon in chat UI

feat: route PDF files to fileToPdfAttachment in addPendingImages

feat: allow PDF files in attachment file picker

fix: remove You/Claude labels from chat message bubbles

feat: add MAX_PDF_BYTES constant and fileToPdfAttachment helper

docs: add PDF upload implementation plan

docs: add PDF upload feature design spec

docs: update README for multi-model config format and model switcher

chore: untrack claude-chat.config.json (contains secrets, covered by .gitignore)

config: set up 5-model configuration for multi-model switching

feat: add model dropdown CSS

refactor: remove API Key/Base URL/Model fields from settings tab

fix: disable single-model button, deduplicate isActive logic