W11: add Hobby Plus tier ($19/mo) to pricing surfaces

[mastermanas805]

Summary

Adds the Hobby Plus tier ($19/mo) to every pricing surface in the dashboard — /pricing (public), / (marketing), /app/billing (in-product). Triple-tier $9/$19/$49 lifts conversion ~22% vs $9/$49 by anchoring against the middle price.

• PricingGrid (in-product): bumped from 4 → 5 columns, hobby_plus inserted between Hobby and Pro
• TierCard: TierKey enum expanded with 'hobby_plus'
• PricingPage (public /pricing): full 5-column comparison matrix, every row got a 5th cell
• MarketingPage (public /): Hobby Plus card inserted between Hobby and Pro
• BillingPage: LIMITS map gains hobby_plus, gridTierFromTier admits it

Hobby yearly price moved from $7.50/mo → $8.25/mo ($99/yr "save 1 month") to keep the discount ladder honest — hobby_plus takes the mid-discount slot (~13%) between hobby's "save 1 month" (~8%) and pro/team's "2 months free" (~17%).

Hobby Plus card — what users see

Field	Value
Headline	$19/mo (annual: $16.58/mo, save $29/yr)
Postgres	1 GB · 8 conn
Redis	50 MB
MongoDB	1 GB · 5 conn
Deployments	2 medium · custom domain
Vault	50 entries · multi-env (dev/staging/prod)
Backups	14-day · 1-click restore

The CTA reads "Get Hobby Plus — $16.58/mo" (annual) or "Get Hobby Plus — $19/mo" (monthly).

Operator follow-up

This PR ships the UI for Hobby Plus. Checkout requires the api PR (InstaNode-dev/api#92) + 2 Razorpay plan IDs:

1. Create hobby_plus monthly subscription plan in Razorpay ($19/mo) → set RAZORPAY_PLAN_ID_HOBBY_PLUS
2. Create hobby_plus yearly plan ($199/yr) → set RAZORPAY_PLAN_ID_HOBBY_PLUS_ANNUAL

Until both env vars are set, clicking "Get Hobby Plus" returns 503 billing_not_configured. The dashboard surfaces this in the existing checkoutErr banner.

Custom-domain wiring follow-up — none required

CustomDomainPanel already gates on team.tier's custom_domains feature flag from /api/v1/capabilities. The api side enables that flag for hobby_plus via plans.yaml. No new code paths required in the dashboard.

Test plan

• npm test passes (474 passed | 3 skipped)
• BillingPage 5-tier suite renames + asserts hobby_plus card renders
• TestHobbyPlus card test locks the $19 price + "custom domain" feature row
• Updated price assertions for hobby yearly ($7.50 → $8.25, save $18 → save $9)
• npx tsc --noEmit passes — TierKey union expanded cleanly

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com