docs: rewrite README as motivation-led; split long-form into docs/

The README was 411 lines and read like a spec. New version (216 lines)
opens with the project's actual motivation in the author's voice,
states what the three views show, and links to deep-dives for the rest.

Moved out of README:
- Verification + Source Matching workflow detail -> docs/source-matching.md
  (the scholarly half is already in CONTRIBUTING.md and ADR 0002).
- Sacred Text Integrity Policy long form -> already in ADR 0001;
  README keeps a 6-bullet summary that links there.
- Long-term roadmap / 6-month plan / phase tables -> docs/research-vision.md.

Added: docs/research-vision.md captures the broader knowledge-graph and
Markdown-vault project (corpus ingestion across all riwayat, HarfBuzz
snapshot QA, scholar review through Mar 2027) that motivates the React
prototype. Preserves the author's positionality framing.

Also fixes stale spots in the previous README: "~30 tests" -> 128;
sampleVariants/fullVariants references in the architecture diagram
replaced with the actual runtime files (quranData, morphologyData,
manuscriptsData, plus the optional git-ignored overlays).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: snesmaeili