feat(ui): Volume Contracts configuration page

[prajjwalkumar17]

What

Dashboard UI for the volume-commitment contract DSL introduced in #367. New Volume Contracts entry in the sidebar's Routing section (beta badge) at /routing/volume-contracts, styled identically to the other routing pages and built from the existing UI kit (Card/InsetPanel/Button/Badge/Combobox/SearchableSelect/ConfirmDialog, SWR + POST fetchers, routing:write permission gating). Stacked on the #367 branch; merge that first.

• Builder covering the full DSL (parameter reference below), with the archetype-specific term blocks switching by archetype and the "exactly one targeted retroactive tier" rule enforced directly in the form (radio per contract; marginal tiers can't be targeted).
• Document list with Active/Inactive badges, expandable stored-JSON view (shows the canonicalized document), and activate / deactivate / delete lifecycle with confirm dialogs — same flow as the Rule-Based page.
• types/api.ts gains VolumeContractConfig types and volume_contract in the algorithm type unions; EuclidRulesPage now excludes volume-contract documents from its rules list (they have their own page).

No new endpoints: everything rides POST /routing/{create,list,list/active,activate,deactivate,delete} with algorithm_for: volume_commitment and algorithm: { type: "volume_contract", data: … }.

DSL parameter reference

Document (merchant-level)

Field	Type	Required	Default	Notes
schema_version	int	no	1	only 1 writable
routing_mode	pace_guarded | volume_commitment	yes	—	Mode 1 / Mode 2
tolerance	"5pp" | "550bps" | int bps	yes	—	stored as tolerance_bps; ≤ 2000 bps
metric	gmv | volume	no	gmv	one metric per merchant
currency.denomination	ISO-4217	yes	—	one currency per document
currency.amount_units	major | minor	no	minor	input units; stored canonicalized to minor
expected_daily_traffic	int | decimal string	yes	—	total across PSPs, > 0
forecast_interval_secs	int	no	engine default	60–604800
steering_interval_secs	int	no	engine default	60–604800
volume_contracts	list	yes	—	1–50 entries

Per-PSP contract

Field	Type	Required	Default	Notes
id	string	yes	—	[A-Za-z0-9_-]{1,64}, unique in document
connector	string	yes	—	exact gateway name routing uses
status	active | inactive	no	active	one active contract per connector
billing_cycle.type	calendar_month | calendar_quarter | calendar_year	yes	—
billing_cycle.anchor	int	yes	—	1–30 / 1–3 / 1–12 by cycle type
billing_cycle.timezone	IANA string	yes	—	validated against tz database
billing_cycle.proration	full_period	no	full_period
archetype	lumpsum | tiered (| min_commitment)	yes	—	B parses but is gated off in v1
scope	—	reserved	—	future euclid-condition cluster scoping; must be absent

lumpsum terms (archetype A)

Field	Type	Required	Notes
target	amount	yes	GMV/count that unlocks the reward, > 0
reward.kind	flat | percentage	yes	tagged enum — mutual exclusion on the wire
reward.value.flat_amount	amount	iff flat	> 0
reward.value.rebate_bps	int	iff percentage	1–10000

tiered terms (archetype C) — per tier

Field	Type	Required	Default	Notes
kind	retroactive | marginal	yes	—	retroactive pays on whole period, marginal above threshold
rate.rebate_bps / rate.rate_bps	int	yes	—	field pairs with kind; 1–10000
threshold	amount	yes	—	strictly increasing across tiers
targeted	bool	one per contract	false	the goal tier the engine steers for; must be retroactive
rebate_lag_days	int	no	0	≤ 365
rebate_settlement	cash | credit_note	no	cash

Amounts are JSON integers or decimal strings in the declared amount_units; the backend stores everything canonicalized to integer minor units. No derived values (goals, rewards, period ends) are computed by the UI or stored — resolution stays the engine's job.

Verified locally

Against a live backend (postgres) + vite: logged in, created a document from the form ($6M target / $15k flat / $800k daily traffic in major units, 5pp tolerance), confirmed the stored JSON came back canonicalized (tolerance_bps: 500, target: 600000000, expected_daily_traffic: 80000000, amount_units: minor), activated it (Active badge, mapper slot), deactivate/delete guarded by confirm dialogs. tsc --noEmit and npm run build green; website/dist regenerated per repo convention.