Feature flags, experiments, UI improvements

[iansinnott]

Feature Flags

The app now includes feature flags. The main motivation here is to be able to ship experimental, potentially breaking changes without breaking the app for anyone. These experiements will be opt in until they seem stable enough to roll out without a flag.

Experiments

Along with the feature flags this PR creates a new experiments page with various things that might be of interest. The first experiment is browser-centric vector search over chat history.

UI Improvements

Small UI improvements. Most notably the controls in the chat window are more compact.

---

• add dev page for experimenting
• add transformers js for creating embeddings
• dev tooling for vec db
• update build script
• add serach icon and focus state to thread searcher
• vecdb initial experiment
• update send icon
• add feature flags
• make command button persistent across pages, update styling
• update github actions
• update db dependencies
• improve feature flags
• add an actions menu item for the dev page
• show schema name on migration failure
• add a migration for supporting vec db
• add vector search to the dev experiments page
• obfuscate api key in debug logs
• refactor vecDb to be available to the whole project
• add progress component
• fix bug in embedding where pipeline was loaded every call
• add loading state to database import
• add a button to get back to main app from sub pages
• update vector store with progress, update vector search ui
• update input styling
• add experimental vector search page
• update dev container styling to not interfere with layout
• refactor feature flags and vector search page
• add a stats page
• update toast strategy
• toast dependencies
• update actions menu
• replace posthog client id
• make experimental tab more searchable
• fix list item styling
• fix overlap issue with dev container