refactor(orpc): unify campaign "counters" naming with project "stats"

[ciokan]

Moved out of studio/TODO.md (see #6).

contract renamed from counters to stats (campaign)

Problem

counters and stats are used inconsistently across the contract schemas.

packages/orpc/src/schema/projects.ts has both, and the split there is meaningful:

stats: z.object({    // engagement metrics
    sent, bounced, opened, replied
}).optional(),

counters: z.object({ // entity counts
    campaigns, leads, leadsLists
}).optional(),

packages/orpc/src/schema/campaigns.ts has a single counters object that mixes both concerns:

counters: z.object({
    sent, opened, clicked, replied, bounced, unsubscribed, delivered, // metrics
    leads, sequences,                                                 // entity counts
})

Proposal

Adopt the projects convention everywhere: stats = engagement metrics, counters = entity counts. On campaigns, split the current counters object into stats (sent/opened/clicked/replied/bounced/unsubscribed/delivered) and counters (leads/sequences).

Open question worth settling in this issue: campaigns_counters (contract + schema + API module, mounted at prefix /campaigns/counters) returns per-day engagement metrics — under the convention above it should be renamed to campaigns_stats / /campaigns/stats.

Scope

• packages/orpc/src/schema/campaigns.ts, schema/campaigns_counters.ts
• packages/orpc/src/contract/campaigns_counters.ts + its registration in contract/index.ts
• apps/api/src/modules/campaigns/controller.ts, modules/campaigns/counters/*, modules/projects/controller.ts
• apps/dashboard/src/enhancers/campaign.ts, components/campaigns/list/list.tsx, components/projects/list.tsx
• Rebuild packages/orpc (+ dbschema if touched) afterwards.

Breaking change to the public route path if /campaigns/counters is renamed — fine while the API is still faker-backed and unreleased.