feat(billing): split volume from rights — add Team and Embed/OEM tiers

## The structural error
The $299 tier fuses two axes that must be separate:
- **Volume** (10k req/day) is a **cost proxy** — scales with our infra bill
- **Redistribution rights** is a **value axis** — scales with the licensee's
business, not ours

An OEM partner may use low volume but need broad rights; a quant fund needs the
opposite. Pricing on volume alone gives away the one thing Dataminr's licence
structurally forbids.

**Rule: self-serve can sell volume; only a human can sell rights.**

## Proposed ladder
| Tier | Price | Rights | Gate |
|---|---|---|---|
| Developer (today's $299) | $299/mo · $2,691/yr | R1+R2 internal + attributed public display | Self-serve |
| **Team** | $999/mo · $9,000/yr | + derived-facts redistribution | Self-serve + click-through addendum. 50k/day, 25 seats |
| **Embed/OEM** | from $2,000/mo · $18,000/yr | + white-label, caching, contractual SLA | **Sales only**, banded |
| **Prime** | floor $75,000/yr | + tender support, evidence pack | Sales only |

## Embed bands (by the partner's end-customer count)
| Band | End-customers | Annual |
|---|---|---|
| Starter | 1-25 | $18,000 |
| Growth | 26-100 | $36,000 |
| Scale | 101-500 | $72,000 |
| Platform | 500+ | floor $112,500 |

Banding beats revenue share (unauditable by a small team, destroys the
99%-recurring quality, and "net revenue" definitional fights are what make data
licensing negotiations run a year) and beats per-seat resale (couples our
revenue to their churn). You verify a **count**, never revenue, and growth
reprices mechanically at renewal: "you've grown into the next band" is a
formality, "we're raising your price" is a fight.

## Three sanity checks, all pass
- Starter = **~$18 per end-customer/yr** — centre of the evidenced $15-30
intel-only band
- Growth ($36k) serves up to 100 downstream clients for **less than one**
Dataminr Pulse Team SKU at $65,000/yr (AWS Marketplace list)
- Starter sits just under the ~$21.5k/$22k Vendr single-org median for
Everbridge and Dataminr — a partner pays roughly one company's CEM budget and
serves 25

## Keep self-serve
`dataminr.com/pricing` is a hard 404 and every deal is a sales call. A working
credit-card path to a real API key is a genuine advantage. Do not gate Developer
behind a call.

## Acceptance
- [ ] Team and Embed tiers in the product catalogue
- [ ] Embed banding + verification mechanism
- [ ] Rights class per tier, matching the ToS
- [ ] Self-serve retained through Team

Effort: L (~7d).

No repository files or tests are named. Start by locating the product catalogue, ToS rights definitions, and the existing self-serve credit-card/API-key path; add Team and Embed/OEM tiers, band verification, matching rights classes, and retain self-serve through Team.

Written by the indexing model from the issue text.