feat(v1): add campaigns, segments, workflows, analytics, usage and v1 events with RFC 9457 errors

[BSalaeddin]

Extends the SDK to Sendly's new `/api/v1` surface (33 operations) plus the two legacy list-subscription ops the re-synced spec surfaced. Additive only — zero breaking changes; 0.2.0 → 0.3.0.

What's new

• Resources: `campaigns` (10 ops incl. send/cancel/pause/resume/stats), `segments` (6), `workflows` (9 incl. executions), `analytics` (3), `usage` (1), v1 methods on `events` (`list`/`record`/`listNames`/`stats` — legacy `track` untouched), and legacy `lists.subscribe`/`unsubscribe` (double-opt-in PENDING/confirmToken and allowResubscribe/409 semantics documented from the spec's own operation descriptions).
• RFC 9457 errors: `/api/v1/*` failures (`application/problem+json`) map onto the same `SendlyError` subclasses as the legacy envelope, with additive `requestId` and `fieldErrors` members; `ProblemDocument`/`ProblemFieldError`/`asProblemDocument` exported. Detection trusts the media type and falls back to document shape — the legacy envelope can never match.
• Cursor auto-pagination: async-generator `*All` companions on the 6 cursor-enveloped list ops, with repeated-cursor loop protection; a contract test derives the cursor-shaped op set from the spec so a future spec change fails closed.
• Idempotency: `IdempotencyOptions` on exactly the two spec-declared v1 ops — `campaigns.create` and `campaigns.send` (the spec deliberately omits the header elsewhere; `events.record` takes none).
• v1 deletes return the typed `{id, deleted}` body; `campaigns.send(id, body?)` supports `{scheduled_for}` scheduling.
• Spec-defect workarounds documented in `src/types.ts` aliases only (map-value narrowing and default-implies-required from the generator) — platform-side fix tracked separately.

Verification

140 tests (18 files) · contract suite green with NOT_YET_IMPLEMENTED empty (all 72 spec ops mapped) · lint 0 warnings · tsc clean · format:check clean · committed dist rebuilt and byte-identical to a fresh build · built-bundle assertions on method arities. Webhook verifier untouched. Release path: tag `v0.3.0` after merge — the tag workflow re-runs the gate and publishes via npm OIDC trusted publishing.

Mirrors DevinoSolutions/sendly-python#3 (same surface contract, cross-language parity reviewed).

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