Give concrete HipError subclasses default messages

[Sarita-Joshi]

What does this PR do?

Constructed without a message, each concrete HipError subclass now uses its own default:

Class	Default
HipBadInputs	Inputs not valid
HipUnauthorized	Unauthorized
HipForbidden	Forbidden
HipNotFound	Resource not found
HipConflict	Conflict
HipInternal	Internal server error

Every string is one the library already put on the wire (mongoose loaders' 404, zod helpers' 422, the lifecycle scrub message), and all in-tree throw sites pass an explicit message — so no response changes.

Why: it binds the HTTP status and the client-visible message to a single symbol, so a caller can pass the class where an error is wanted and do new DenialError() at each throw site. A reusable authorization gate then gets a fresh error with its own stack per denial, instead of sharing one prebuilt instance across every request or wrapping the constructor in a factory thunk:

function requireOwner(DenialError: new () => HipError = HipForbidden) { /* … */ }
requireOwner(HipNotFound); // denial answers exactly as a missing row does

An explicit message still wins, including an empty one (??, not ||), and a subclass that declares no default behaves exactly as before.

INTERNAL_ERROR_MESSAGE moves to ./errors.js (it is HipInternal's default) and is re-exported from ./core.js, so existing imports are unaffected — verified identical from hipthrusts, hipthrusts/core and hipthrusts/errors in both the CJS and ESM builds.

Wire change worth noting: a bare new HipForbidden() previously produced {"error":""} and now produces {"error":"Forbidden"}. That's the point of the change, but it is visible — additive/minor.

No version bump — releases are cut as their own PR.

Checklist

• Tests added/updated (type-level tests for changes to the type machinery)
• pnpm test, pnpm lint, pnpm typecheck, and pnpm build pass locally
• Docs updated (README / examples) if the public API changed

Also ran pnpm format:check, pnpm check:exports, pnpm smoke — all clean; 241 tests pass.

🤖 Generated with Claude Code

[trycatchal]

lgtm! thanks!