docs: add UI screenshots to the README

[CMaintz]

The README only had the storyboard SVG. These are real screens: dashboard, pipeline and a company's research notes.

How I got them, since the app needs Firebase and an OpenAI key:

• Firebase Auth emulator plus a throwaway service account, with connectAuthEmulator patched in locally (not committed).
• Dummy OpenAI key and the crawler/LinkedIn/sweep schedules switched off, so nothing hit real job boards and no AI output appears.
• Made-up user, companies and postings, added through the API with a bit of SQL for statuses and company links.

Caveats:

• main doesn't boot right now (the AI usage query bug), so I ran the backend from fix(backend): make company research notes per user #169, which includes fix(backend): search and AI usage queries broken on Postgres #160's fix.
• The dashboard greeting was a raw i18n key; the screenshot has the fix from fix(frontend): add the missing dashboard greeting strings #170 applied.

This merged with the hardcoded "12-day streak" still visible; #175 retakes the screenshots now that #172 makes the streak real.