Strip duplicated JSON blocks from component analysis Markdown

[ethenotethan]

Summary

• The component-analyzer has been emitting two fenced JSON blocks in every
  .md — ## Citations and ## Analysis Data — that duplicate (or go
  unread by) other artefacts. Strip them from the Markdown after extraction
  so the human-facing analysis stays prose-only.
• ## Citations is already lifted into {component}.citations.json by the
  citation extractor, with richer content (source_repo, source_commit,
  citation_count, per-citation source_url). The Markdown copy was pure
  duplication.
• ## Analysis Data was never consumed anywhere downstream — no extractor,
  no reader, no test. Pure dead weight.

Details

agent/utils/citation_extractor.py

• New public strip_extracted_sections(md) helper: idempotent, collapses
  blank-line runs left behind, normalises trailing newline.
• build_citations_index invokes it in-place after each successful
  per-component sidecar write. Gated on success — if the ## Citations
  block fails to parse, the block is left in the .md so malformed
  content is still visible for debugging.

agent/discovery/validator.py

• _validate_citations_in_file → _validate_citations_sidecar. Reads
  {component}.citations.json instead of regex-parsing the Markdown
  (since the block is no longer guaranteed to be there after extraction).
• Spot-check logic unchanged — the citation dict shape in the sidecar is
  identical to the former Markdown JSON.

tests/test_citations.py

Seven new tests covering:

• Strip helper behaviour (strips both sections, idempotent, preserves
  ## Analysis Summary as a false-positive guard, no-op on clean input,
  trailing-newline normalisation).
• End-to-end build_citations_index contract: Markdown stripped only
  when the sidecar was successfully written; Markdown untouched when
  extraction fails.

Impact

• api.md dropped from 209 → 115 lines (~3.7 KB) after cleaning. Similar
  reductions across all 11 components in the omlx run.
• All 254 tests pass (.venv/bin/python -m pytest -x -q).
• No information loss: every field in the former Markdown ## Citations
  block is present (and enriched) in the sidecar JSON.

Out of scope

Noticed while investigating but not fixed here: the architecture
documenter emits the raw templates/architecture_template.md largely
unfilled (placeholders like {For each: ...} left in place, the
illustrative "User Registration Flow" example copied verbatim).
Separate issue, separate PR.