docs: expand data-license disclaimers

[hobbyistz]

Broadens LICENSE-DATA.md section 4 (now "No warranty; no advice; limitation of liability"):

• "as is", informational purposes only, no warranty of accuracy, completeness, or fitness for any particular use
• express limitation of liability, including indirect/consequential damages and lost profits, to the maximum extent permitted by law
• no guarantee of continuous or uninterrupted publication
• notice that the index is computed from publicly available provider prices whose continued availability is outside Computable's control, with sources and panel membership subject to change per METHODOLOGY.md and GOVERNANCE.md

No change to the base CC BY-NC 4.0 grant, the Section 2 Product Use reservation, or the machine-readable license block.

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