Publish radar to Pulse — single slug, two share toggles

[fleveque]

First of two coordinated PRs to add "share your radar on Pulse" alongside the existing portfolio sharing. This PR is the Quantic side (schema + NATS publishing + Settings UI). Pulse-side consumer + worker + LiveView + dashboard aggregates ship next as a separate PR.

Sharing model

One slug per user (existing portfolio_slug) with two booleans:

• share_portfolio — default true (back-compat, current sharers keep sharing)
• share_radar — default false (opt-in for the new surface)

When both are enabled: pulse.quantic.es/p/<slug> AND pulse.quantic.es/r/<slug>.

Publish flow (mirrors portfolio path)

• User#publish_pulse_changes (renamed from publish_portfolio_slug_change) — fires on save when slug, share_portfolio, or share_radar changed. Diffs the effective shared state per surface and emits {portfolio,radar}.opted_in/out correctly across all 6 transitions.
• RadarStock#after_commit :publish_radar_updated — re-emits radar.updated on any radar change (add / remove / target_price edit). Mirror of Holding#publish_portfolio_updated.
• RadarPayloadBuilder (new) — v1 payload with enough stock metadata (price, dividend_yield, 52w range, MA200) that Pulse can render a standalone radar page without portfolio events.

Settings UI

Existing Share on Pulse card gets a "What to share publicly" subsection (visible only when a slug is set) with two checkbox rows. New ShareToggle component shows the live public URL per surface when enabled.

Frontend polish (added after initial scope)

• Localized stock sectors via new translateSector(t, sector) helper + sectors namespace in both en.ts / es.ts. Covers the 17 GICS / Yahoo Finance names + Unknown; unknown sectors pass through verbatim. Wired into PortfolioStatsCard's sector legend and tooltip.
• Pulse share button on the radar page. PulseShareButton parameterised with kind: 'portfolio' | 'radar' — gates on the matching toggle (sharePortfolio / shareRadar) and links to the right URL. Also fixed: if a slug exists but the relevant toggle is off, show the "opt in from Settings" hint instead of a dead public link.
• Radar AI insights title said "AI Portfolio Insights" because RadarInsights and PortfolioInsights shared the insights.title key. Split into insights.portfolioTitle and insights.radarTitle.

Deploy order: ship the Pulse PR first

NATS is plain pub/sub (no JetStream queue) — messages sent to a subject with no live subscriber are dropped at the broker. If this PR deploys before fleveque/pulse#35:

• radar.opted_in events for users toggling Share Radar are dropped — their radar never registers in Pulse until they next edit it.
• radar.updated events from price refreshes are also dropped during the window.

Order to ship: fleveque/pulse#35 first (Pulse starts subscribing to radar.* and idles harmlessly with no publishers), then this PR (Quantic starts publishing into a Pulse that's ready to consume from event #1).

Test plan

• bundle exec rspec — 676 examples / 0 failures (22 new across payload builder, user transitions, RadarStock callback, profile controller)
• bin/rubocop on touched Ruby — clean
• npx tsc --noEmit — clean
• npx vite build — succeeds
• Manual: Settings → toggle Share radar → publish appears in NATS monitoring (localhost:8222)
• Manual: edit a target price → radar.updated fires
• Manual: clear portfolio_slug → both opt-out events fire
• Manual: switch language to ES → sector names render in Spanish; radar page shows "Compartir en Pulse" + "Análisis IA del Radar"

Rollback

Single revert. Migration adds two columns with safe defaults — leaving them in place is harmless if code reverts.

Sister PR

Pulse-side (RadarWorker + RadarLive + Dashboard "Community watchlist"): fleveque/pulse#35.

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