feat(postman): upgrade to IR v66

[Swimburger]

Description

Upgrades the Postman generator to IR v66, which compresses the Name type into a NameOrString union (plain string or full Name object). All generator source code is updated to use runtime helpers (getWireValue(), getOriginalName(), CaseConverter) for transparent handling of both compressed and uncompressed name formats.

Changes Made

v66 IR Handling

• Replaced all direct .wireValue accesses with getWireValue() helper (auth headers, query params, example headers)
• Replaced all direct .originalName accesses with getOriginalName() helper (error names, subpackage names, endpoint names, path params, API name)
• Replaced direct .camelCase.unsafeName / .screamingSnakeCase.unsafeName accesses with CaseConverter methods
• Added CaseConverter instances in auth.ts and AbstractGeneratedRequest.ts

New IR Union Variants

• Added inferred auth scheme handler in auth.ts and convertToPostmanCollection.ts
• Added bytes response body handler in convertExampleEndpointCall.ts
• Added head HTTP method handler in AbstractGeneratedRequest.ts (mapped to GET — PostmanMethod enum lacks HEAD)
• Added filesystem publish target handler in writePostmanCollection.ts
• Added type guard for publishConfig.target before accessing postman-specific fields

Version & Migration

• Added 0.7.0-rc.0 entry to generators/postman/versions.yml with irVersion: 66
• Registered POSTMAN → "0.7.0-rc.0" in migrateFromV66ToV65.ts
• Updated seed/postman/seed.yml irVersion from v53 to v66

Testing

• Unit tests added/updated
• Manual testing completed
• Seed tests pass with irVersion: v66

Human Review Checklist

• IR migration mapping updated in migrateFromV66ToV65.ts
• Seed test config updated to target v66 IR
• All .wireValue / .originalName / casing accesses migrated to helper functions
• pnpm-lock.yaml inconsistency: The lock file diff shows @fern-fern/ir-sdk changed to 66.0.0-alpha.1, but package.json was reverted to 53.9.0. The lock file may need to be regenerated (pnpm install) to stay in sync.
• HEAD → GET mapping (AbstractGeneratedRequest.ts:102): PostmanMethod enum lacks HEAD, so head is mapped to PostmanMethod.Get as a workaround. Verify this is acceptable or if the Postman SDK should be extended.
• Confirm version bump 0.6.1 → 0.7.0-rc.0 follows the correct convention for this generator

Link to Devin session: https://app.devin.ai/sessions/1947204928ba4bfe9b663dfe828ac3d7
Requested by: @Swimburger

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