feat(ir): add webhook body param sort specification to CLI and IR

[iamnamananand996]

Description

Linear ticket: Refs FER-8930

Adds a body-sort option to WebhookPayloadFormat so that POST body parameters can be sorted alphabetically by key before concatenation into the signing payload. This is required by providers like Twilio.

Changes Made

• IR schema: Add optional bodySort field (WebhookPayloadBodySort enum with ALPHABETICAL) to WebhookPayloadFormat
• OpenAPI IR schema: Mirror the same field/enum (lowercase alphabetical)
• Fern Definition schema: Add body-sort field and WebhookPayloadBodySortSchema enum
• Regenerated TypeScript types for all three schemas (pnpm ir:generate, fern generate --local)
• Regenerated JSON schemas (fern.schema.json, package-yml.schema.json, and lazy-fern-workspace copies) via pnpm definition-yml:jsonschema and pnpm package-yml:jsonschema
• OpenAPI parser (getFernWebhookSignatureExtension.ts): Parse body-sort from x-fern-webhook-signature extension's payload-format block
• IR generator (convertWebhookGroup.ts): Pass bodySort through in convertPayloadFormat
• OpenAPI IR→Fern converter (buildWebhooks.ts): Convert bodySort back to body-sort
• Test fixture & snapshots: Updated x-fern-webhook-signature fixture with body-sort: alphabetical, regenerated OpenAPI IR snapshots, Fern definition snapshots, ETE IR snapshot, and IR generator test snapshots (webhooks.json, audiences.json, environmentAudiences.json)
• CLI changelog: v4.32.0 feat entry

Note: The exhaustive.json snapshot diffs (both ir/__test__/test-definitions/exhaustive.json and dynamic-snippets/__test__/test-definitions/exhaustive.json) are pre-existing changes from main (renaming getAndReturnWithDocumentedUnknownType → getAndReturnMapOfDocumentedUnknownType and adding MapOfDocumentedUnknownType). They are unrelated to this feature and were picked up during snapshot regeneration.

IR Migration (v65→v63)

No migration changes needed — the existing v65→v63 migration already strips signatureVerification entirely from webhooks, so the nested bodySort field is implicitly removed.

Human Review Checklist

• Verify the v65→v63 migration correctly handles the new bodySort field (it strips signatureVerification entirely, so bodySort inside WebhookPayloadFormat should be dropped)
• convertBodySort in getFernWebhookSignatureExtension.ts has no default case (relying on TS exhaustiveness), while buildWebhooks.ts has default: return undefined. Confirm this inconsistency is acceptable or align them
• ETE and IR generator test snapshots show "bodySort": null for webhooks that don't set body-sort — confirm this is expected (JSON serialization of undefined → null)
• Verify convertPayloadFormat in convertWebhookGroup.ts now passes bodySort: undefined in the default (null payloadFormat) branch — confirm this doesn't break downstream consumers
• Confirm the unrelated exhaustive.json snapshot diffs (IR + dynamic-snippets) are safe to include

Testing

• pnpm run check (biome lint/format) passes locally
• Snapshot files updated for x-fern-webhook-signature fixture (OpenAPI IR + Fern definition)
• ETE IR snapshot regenerated via vitest --update for webhooks test
• IR generator test snapshots regenerated (webhooks.json, audiences.json, environmentAudiences.json)
• JSON schema files regenerated (fern.schema.json, package-yml.schema.json)
• CI seed tests (prior failures were Docker Hub 504 Gateway Time-out, not code-related)

Link to Devin session: https://app.devin.ai/sessions/b8c7736ece704d12b0bec3014be4bc84
Requested by: @iamnamananand996

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