feat(trpc): standard error formatting for high-throughput indexer API

[samkay-ops]

Summary

Implements standard tRPC error formatting for the Fastify indexer API (#598).

Previously HTTP/batch handlers returned ad-hoc { error, message } payloads and often leaked internal Error.message values. Procedures also threw plain Errors.

Changes

• Add errors.ts with toTRPCError, formatTRPCErrorShape, and helpers
• Enable errorFormatter on the shared initTRPC instance (optional zodError)
• Normalize batch + single HTTP catch paths to tRPC-shaped errors + correct HTTP status
• Throw TRPCError for unknown procedure / unsupported subscription
• Unit tests for mapping, sanitization, and wire shape

Acceptance criteria

• Execution stays non-blocking (sync mapping only; no extra I/O on the error path)
• Edge cases / malformed inputs map to BAD_REQUEST or NOT_FOUND without crashing the process
• Internal failures return a generic message; details stay in server logs
• Response shape is consistent for single and batch calls
• Type-safe TRPCError boundary preserved

Closes #598