dropthejase rips out Supabase for Aurora

All LLM calls go through Bedrock IAM - no user API keys, no credits,
no tabular model stored per user. Removes UserApiKeys type, claude/gemini
key columns from userSettings, credits/tier/tabularModel fields from
UserProfileContext, and the ApiKeyMissingModal/modelAvailability shims
that were never reachable. TRChatPanel now holds model as local state.

Deleted backend/src/routes/projectChat.ts entirely (POST /projects/:projectId/chat
streaming handler - frontend calls AgentCore directly). Removed its import and
app.use line from app.ts.

Removed the POST /chat/ streaming handler from chat.ts and its exclusive imports
(chatTools functions and checkCredits). Note: chatTools.ts is retained because
tabular.ts still actively uses runLLMStream, TABULAR_TOOLS, ChatMessage, and
TabularCellStore from it.

Dropped chat_messages and tabular_review_chat_messages from Aurora
(both empty; history lives in S3 snapshots). Removed dead
hydrateEditStatuses() function and chat_messages SELECT from
GET /chat/:chatId. Issue 26 documented in TEMP_TASKS for future
edit status hydration on S3 history load.