feat: add user-agent prefix input

[goanpeca]

Summary

• Add a user-agent-prefix input to action.yml, README, and the generated action bundle.
• Thread the optional prefix through parsed inputs into the SDK B2Client userAgent, preserving the default b2-github-action/<version> token and treating blank prefixes as unset.
• Validate prefixes before client construction with a 128-byte UTF-8 limit and visible ASCII-only policy, rejecting control characters, DEL, tab, non-ASCII/surrogate payloads, spaces, and oversized values with parser errors.
• Measure prefix byte length with Buffer.byteLength(value, 'utf8') to avoid allocating encoded bytes during validation.
• Document the final User-Agent format, accepted character contract, changelog entry, and a copyable repository/workflow traceability example.
• Cover configured, absent, blank, and invalid prefixes in tests, and rebuild dist.

Linked issue

• Part of Expose remaining B2 SDK capabilities in the action (tracking) #106.

Tests run

• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm docs:check-action-yml
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm docs:lint
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm cspell README.md
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm vitest run __tests__/inputs.test.ts __tests__/client.test.ts __tests__/main.test.ts
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm vitest run __tests__/inputs.test.ts
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm lint
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm typecheck
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm run docs
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm test
• /Users/gpenacastellanos/miniforge3/condabin/conda run -n b2-action-issue-106 pnpm build
• pre-commit hook: lint, release provenance, typecheck, vitest, ncc build, cspell
• pre-push hook: vitest --coverage

Follow-up notes

• Remaining SDK-parity checklist items in Expose remaining B2 SDK capabilities in the action (tracking) #106 are unchanged.

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[Copilot]

Pull request overview

Adds a new optional user-agent-prefix input so workflows can prepend a traceable marker to the action’s User-Agent string while keeping the action’s default b2-github-action/<version> token, including validation to prevent HTTP header control characters and rebuilding dist/.

Changes:

• Introduces user-agent-prefix in action.yml and documents it in README.md.
• Parses and validates the new input (rejecting control characters) and threads it through to buildClient.
• Updates buildClient to prepend the prefix to the action User-Agent token, and adds/updates unit tests and dist/ output.

Reviewed changes

Copilot reviewed 9 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/main.ts	Conditionally passes userAgentPrefix into client construction only when provided.
src/inputs.ts	Adds userAgentPrefix to parsed inputs and validates it for HTTP-header safety.
src/client.ts	Builds the SDK userAgent string with optional prefix + action token.
action.yml	Exposes the new user-agent-prefix input to action consumers.
README.md	Documents the new input and warns not to include secrets.
tests/inputs.test.ts	Tests parsing and rejection of control characters for the new input.
tests/main.test.ts	Tests that buildClient receives userAgentPrefix when present.
tests/client.test.ts	Tests that the constructed SDK options include the prefixed User-Agent.
tests/_parsed-inputs.ts	Updates the parsed-inputs fixture to include userAgentPrefix.
dist/index.js	Rebuilt distribution output reflecting the new input and User-Agent behavior.

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