fead(did web): Use Credo's core DID document construction methods

[rmlearney-digicatapult]

Pull Request

Checklist

• Have you read Digital Catapult's Code of Conduct?
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

PR Type

Please delete options that are irrelevant.

• Feature

Linked tickets

High level description

Replace hand-written document construction and validation with native Credo helpers

Detailed description

Credo exports multiple helper methods and validators for DID Document construction.

Swapped existing validation, key construction, document assembly using JsonTransformer and TypedArrayEncoder etc. for these methods.

Added simple did:web input parsing regression test.

Describe alternatives you've considered

Operational impact

Additional context

[Copilot]

🟡 Changes recommended

The new builder path omits document validation, allowing malformed service endpoints.

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Pull request overview

Replaces custom DID:web document construction with Credo-native parsing, key, service, and builder APIs.

Changes:

• Builds DID documents using Credo helpers.
• Adds DID method validation and regression coverage.

File summaries

File	Description
tests/unit/didWebGenerator.test.ts	Tests rejection of non-web DIDs.
src/utils/didWebGenerator.ts	Refactors DID:web generation to Credo APIs.

Review details

Suppressed comments (1)

tests/unit/didWebGenerator.test.ts:77

• The added test passes a syntactically valid did:key, so it only covers the wrong-method branch. Add a malformed input case to protect the new parseDid error wrapping and its Invalid DID identifier message.

      await didWebDocGenerator.generateDidWebDocument('did:key:z6Mkexample', 'http://localhost%3A5002')

• Files reviewed: 3/4 changed files
• Comments generated: 1
• Review effort level: Balanced

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[jonmattgray]

[MINOR] There's no test for the new parsedDid.did !== didId guard — e.g. a did:web identifier with an extra path or query segment. Worth adding alongside the two new tests here since it's the other half of the validation this PR introduces.