Fix bugs, UI tweaks, and update DB reset script

[eteitelbaum]

Summary

• Fix multi-position job visibility: Jobs with multiple positions no longer disappear from "Posted Jobs" after the first contract deploys. Backend now checks positions_available before transitioning status; frontend also shows in_progress jobs with open positions as a safety net.
• Fix idle timeout logout: Warning modal appeared but logout never fired. Root causes: async onTimeout wasn't awaited (unmount race), and onTimeout in useCallback deps caused React StrictMode to restart timers. Fixed with onTimeoutRef + async/await.
• Update DB reset script: Added 7 missing tables (deployed_contracts, payment_transactions, oracle_verifications, dispute_history, mediators, contract_templates, job_postings) to resetDb.js and DATABASE_RESET.md.
• UI tweaks: Fix positions helper text, scrollable admin employer review, reorder oracle display on employer landing page.
• Notes: Add master plan and mark resolved todos.

Test plan

• Employer landing page: oracles display as Manual, Time Clock, Image, Weight, GPS, Custom
• Admin employers page: company description scrolls instead of truncating
• Job creation wizard: positions helper text reads "Enter the number of workers you need for this role"
• Idle timeout: warning appears after inactivity, auto-logout fires when countdown expires
• Multi-position jobs: job stays visible in Posted Jobs after first contract deploys (requires multi-position test data)

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