[Phase 0] Refactor raw storage to source-agnostic paths

[dcaribou]

Type: feature
Suggested labels: phase-0, architecture, ingestion

Standardize raw layout as data/raw///... and remove hard-coded Transfermarkt assumptions from acquisition entrypoints.

Acceptance criteria:

• scripts/acquiring scripts support explicit --source or source-specific script naming with shared conventions.
• Existing Transfermarkt acquisition remains backward compatible.
• README docs updated with new convention.

Dependencies: #1