feat(web): add goal-based first-run onboarding

[federicodeponte]

Summary

• replace the first-open blank-worker surface with one goal question and four task lanes
• map every lane to a prefilled, live Floom gallery template
• make a clearly labeled sample-data run the primary path, with connection setup secondary
• import the selected template and continue to the existing real run page and connection pre-flight
• expose the same first-open path on desktop and mobile without adding flags, experiments, or backend surface area

Goal mappings

Goal	Floom template
Outreach & Leads	@fede/partnership-signal-outreach
Inbox & Comms	@fede/gmail-inbox-cleaner
Research	@fede/meeting-prep
Reports & Dev	@fede/slack-weekly-recap

Verification

• npm test: 204 files passed, 1,016 tests passed, 1 skipped
• npm run lint: 0 errors, 21 pre-existing warnings
• npm run build: production build completed, including TypeScript and route generation
• npm run lint:emdash: passed
• focused onboarding suite: 4 files, 18 tests passed after final lifecycle cleanup
• desktop and fresh-mobile browser QA covered goal selection, template preview, sample result, CTA hierarchy, and composer suppression
• git diff --check: passed

Preview

• Vercel Preview
• Deployment dpl_GDNsB5NWzy5RKkSYtskzawJD1r1Z is Ready with target preview
• Built from engine SHA 99ba8268bf4d6936432d0f06c5a3675ec5edd450 through the cloud sync-engine-web path

Review note

This PR is intentionally review-only. Do not merge until Federico has reviewed the Vercel preview.

[federicodeponte]

Merge-queue FAIL resolved as a pre-existing Windows concurrency flake. This PR changes only eight web onboarding files and does not touch the failing SQLite test, database connection code, fixtures, workflow, or Python runtime. The failed job hit sqlite3.OperationalError: database is locked while enabling WAL during parallel import after 850 tests passed. I reran the failed job on the unchanged head 477ee4a11ff19520dc1be76d32332ae7f1e72b61; Windows runtime tests passed: https://github.com/floomhq/floom/actions/runs/29732616913/job/88416757515. All seven PR checks are now green.