fix: align API names with Swift guidelines

[julianschiavo]

• Rename the exact-entry lookup API to entry(for:) and the CLI command to get for clearer use-site semantics.
• Align package and private bridge names with Swift API design guidelines by removing implementation-heavy terms like stringIdentifier, stringNamed, and locate....
• Add regression coverage for the CLI rename and update docs and integration tests to match.

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Note

Medium Risk
Medium risk because it introduces breaking renames across the public Swift API and xcdocs CLI subcommand, which can disrupt downstream callers despite minimal logic changes.

Overview
Renames the exact-entry lookup surface from fetch to entry across the Swift API (Client.fetch → Client.entry(for:)), the support layer (VectorSearchClient.fetch → entry(for:)), and the CLI (xcdocs fetch → xcdocs get), updating README and integration tests accordingly.

Aligns internal/bridge naming with Swift conventions by replacing implementation-heavy terms (e.g., stringIdentifier → identifier, stringNamed → stringAttribute(named:), locateDatabaseDirectoryURL() → databaseDirectoryURL()), and adjusts related call sites/parameter labels (including MADServiceObject.performRequests).

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