feat: add epic support to get_record

[BeyondRoadmap]

Summary

get_record currently supports features (DEVELOP-123) and requirements
(ADT-123-1) but rejects epic references (DCOMMS-E-157) with an
InvalidParams error. search_documents with searchableType: "Epic"
already works and returns valid epic references — but there's no way to
fetch their content.

This PR adds epic support to get_record so references like DCOMMS-E-157
and CLAIMST-E-474 resolve to their name and description body.

Changes

• src/types.ts — add EPIC_REF_REGEX and EpicResponse interface
• src/queries.ts — add getEpicQuery using the epic(id) GraphQL resolver
• src/handlers.ts — import epic types/query, add epic branch in handleGetRecord
• src/index.ts — update get_record description to mention epics

Notes

• The epic regex does not conflict with existing patterns:
  • Features: PRODUCT-123 (digits only after hyphen)
  • Requirements: PRODUCT-123-1 (two numeric segments)
  • Epics: PRODUCT-E-123 (literal E segment)
• No breaking changes — existing feature and requirement behavior is unchanged
• search_documents with searchableType: "Epic" already works; this
  closes the gap between finding an epic and reading it

Closes #20