[Phase 0] Update repositioning docs with MVP evidence

[dcaribou]

Type: feature
Suggested labels: phase-0, docs, branding

Update README and docs to reflect canonical multi-source identity, and showcase OpenFootball as first non-Transfermarkt integration.

Acceptance criteria:

• README title/subtitle and architecture section reflect new positioning.
• New section explains source lineage and field-level provenance.
• New section links to coverage/quality outputs from MVP pipeline.

Dependencies: #7, #8, #10