chore: workplan MRKD-WP-0001 + improved CLAUDE.md; document next steps

- workplans/MRKD-WP-0001-foundation-level1.md: 8-task workplan for
  Foundation & LEVEL1 Core (T01 scaffolding through T08 e2e harness)
- CLAUDE.md: added Planned Architecture section (interface table, FR
  domain map, key concepts, round-trip data flow) and Development
  Commands stubs derived from FRS v0.2
- problems/next-steps-2026-03-14.md: implementation guide for next
  session — task order, dep list, state-hub task UUIDs, quality gates

No code implemented yet; workstream registered in State Hub.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/conftest.py

@@ -0,0 +1,63 @@
+"""Shared test fixtures for markidocx tests."""
+
+from __future__ import annotations
+
+import textwrap
+from pathlib import Path
+
+import pytest
+
+
+SIMPLE_MARKDOWN = textwrap.dedent("""\
+    # Hello World
+
+    This is a paragraph with **bold** and *italic* text.
+
+    ## Section One
+
+    - Item one
+    - Item two
+    - Item three
+
+    ### Subsection
+
+    Some text with a [link](https://example.com) and `inline code`.
+
+    ## Section Two
+
+    | Column A | Column B | Column C |
+    |----------|----------|----------|
+    | row1a    | row1b    | row1c    |
+    | row2a    | row2b    | row2c    |
+
+    1. First ordered item
+    2. Second ordered item
+    3. Third ordered item
+""")
+
+SIMPLE_MANIFEST_YAML = textwrap.dedent("""\
+    project:
+      name: "Test Document"
+      feature_level: level1
+      family: article
+
+    sources:
+      - path: doc.md
+
+    output:
+      dir: ./dist
+
+    metadata:
+      title: "Test Document"
+      author: "Test Author"
+      date: "2026-01-01"
+""")
+
+
+@pytest.fixture()
+def tmp_project(tmp_path: Path) -> Path:
+    """Create a minimal project directory with a manifest and source file."""
+    (tmp_path / "doc.md").write_text(SIMPLE_MARKDOWN, encoding="utf-8")
+    (tmp_path / "manifest.yaml").write_text(SIMPLE_MANIFEST_YAML, encoding="utf-8")
+    (tmp_path / "dist").mkdir()
+    return tmp_path