feat: add platform fee rules API endpoints and documentation

Introduce a complete CRUD API for platform-configurable fee markup,
enabling platforms to define per-transaction-type fees that layer on
top of Lightspark and counterparty fees.

New endpoints:
- POST /fee-rules — create a fee rule (one per transaction type)
- GET /fee-rules — list all fee rules with optional filters
- GET /fee-rules/{feeRuleId} — retrieve a single rule
- PATCH /fee-rules/{feeRuleId} — partial update (amounts, enabled)
- DELETE /fee-rules/{feeRuleId} — remove a rule
- GET /fee-rules/report — monthly aggregated fee revenue

New schemas:
- FeeRule, FeeTransactionType, FeeRuleType
- FeeRuleCreateRequest, FeeRulePatchRequest
- FeeReport, FeeReportLine

Extended existing schemas:
- OutgoingRateDetails and IncomingRateDetails gain platform fee
  fields (platformFixedFee, platformVariableFeeRate,
  platformVariableFeeAmount) so quotes and transactions surface the
  platform markup alongside Lightspark fees.

New error codes:
- INVALID_FEE_RULE (400), INVALID_MONTH_FORMAT (400)
- FEE_RULE_NOT_FOUND (404), FEE_RULE_EXISTS (409)

Documentation:
- Shared snippet with guide, cURL examples, and fee layering table
- Wrapper pages in all four use-case tabs (Payouts, Ramps, Rewards,
  Global P2P) under Platform Tools

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: jaymantri

mintlify/docs.json

@@ -101,6 +101,7 @@
           {
             "group": "Platform Tools",
             "pages": [
+              "payouts-and-b2b/platform-tools/fee-rules",
               "payouts-and-b2b/platform-tools/webhooks",
               "payouts-and-b2b/platform-tools/sandbox-testing",
               "payouts-and-b2b/platform-tools/postman-collection"
@@ -146,6 +147,7 @@
           {
             "group": "Platform Tools",
             "pages": [
+              "ramps/platform-tools/fee-rules",
               "ramps/platform-tools/webhooks",
               "ramps/platform-tools/sandbox-testing",
               "ramps/platform-tools/postman-collection"
@@ -189,6 +191,7 @@
           {
             "group": "Platform Tools",
             "pages": [
+              "rewards/platform-tools/fee-rules",
               "rewards/platform-tools/webhooks",
               "rewards/platform-tools/sandbox-testing",
               "rewards/platform-tools/postman-collection"
@@ -237,6 +240,7 @@
           {
             "group": "Platform Tools",
             "pages": [
+              "global-p2p/platform-tools/fee-rules",
               "global-p2p/platform-tools/webhooks",
               "global-p2p/platform-tools/sandbox-testing",
               "global-p2p/platform-tools/postman-collection",

mintlify/global-p2p/platform-tools/fee-rules.mdx

@@ -0,0 +1,10 @@
+---
+title: "Platform fee rules"
+description: "Configure the markup your platform charges customers per transaction type"
+icon: "/images/icons/settings-gear2.svg"
+"og:image": "/images/og/og-global-p2p.png"
+---
+
+import PlatformFeeRules from '/snippets/platform-fee-rules.mdx';
+
+<PlatformFeeRules />