[InDesign pipeline] IDML parser and intermediate representation

[PAMulligan]

Sub-issue of #62.

Summary

Implement a parser that reads InDesign Markup Language (.idml) packages and emits a normalized intermediate representation (IR) that downstream stages (mapper, component generator) consume.

Details

• Treat .idml as a zip package; extract and validate manifest, designmap.xml, Resources/, Stories/, Spreads/, MasterSpreads/.
• Parse stories (text + character/paragraph style references), spreads (frames, positions, transformations), master spreads, swatches, fonts, and linked/embedded images.
• Resolve cross-references between stories and frames (ParentStory, Self IDs).
• Normalize units to pixels at a configurable DPI (default 96).
• Emit a typed IR (TypeScript types in packages/pipeline/src/indesign/ir.ts) covering: Document, Spread, Page, Frame, TextFrame, Story, ImageFrame, Style, Swatch, Font, MasterSpread.
• Surface parse warnings (unsupported features) without aborting.

Acceptance Criteria

• Given a fixture .idml, the parser produces a valid IR object that passes schema validation (zod).
• All swatches, paragraph styles, character styles, and fonts are enumerated in the IR.
• Image frames reference resolvable asset paths inside the IDML package.
• Unit tests cover happy path + at least three malformed/edge-case IDMLs.
• Parse warnings are collected on the IR and surfaced by the CLI.

Dependencies

• None (foundational sub-issue)

References

• Adobe IDML File Format Specification