feat(oracle): integrate Recruiting Cloud provider and CLI

[amikai]

Context

Oracle Recruiting Cloud is a multi-company ATS whose public Candidate Experience URLs expose a site alias while API requests may require a different internal site number. A generated API client alone is not enough for reliable manual verification, so this PR adds the discovery and site-bound provider layer plus a CLI aligned with the repository's other multi-company providers.

What changed

• add and validate a minimal OpenAPI contract for anonymous Oracle job search and detail
• generate the ogen client and cover it with captured Hurl fixtures and a mock server
• discover API origin, site alias, internal site number, and language from public Candidate Experience pages
• add site-bound search, facet filtering, pagination, and job-detail operations
• add the curated Oracle company roster used by the shared multi-company CLI convention
• add oracle companies, search, facets, and detail commands
• accept --company as either a curated company name or a full Oracle careers URL; URL discovery stays internal instead of being a separate CLI command
• add fixture-backed CLI end-to-end tests and validation/error-path coverage

Impact

Developers can now inspect curated Oracle companies and exercise search, facets, and detail end to end from the CLI using the same command shape as other providers. The ATS adapter and MCP registration remain a later stage.

Validation

• go test ./...
• go test ./cmd/oracle ./internal/provider/oracle
• gopls check cmd/oracle/main.go cmd/oracle/main_test.go
• go run ./cmd/oracle --help
• go run ./cmd/oracle companies --format text
• live Mayo Clinic search by curated company name
• live Mayo Clinic search by full Candidate Experience URL
• git diff --check

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