Publish heatNumber + sequenceOrLotNumber (successor of castLotNumber) for DPP steel v0.0.2 (#128)

[stiebitzhofer]

Second, small batch for the DPP steel content specification v0.0.2 (material-identity/schema#370), following the certification review of v0.0.2.

Entry	Kind	Note
`heatNumber` (`1789b4b0…`)	new, SingleValuedDataElement, xsd:string	The identifier a steel producer assigns to one heat. Melt-and-pour evidence (Reg (EU) 2026/1384) is tied to it, and v0.0.2 had no heat element.
`sequenceOrLotNumber` (`2f0d456a…`)	successor, `replaces` castLotNumber `c0872ffd`	castLotNumber took "cast" as a sequence of heats, but EN 10204/EN 10168 English usage has "cast number" = the heat. The successor names a casting sequence or a production/processing lot and states that it is not the heat.

Deliberately absent on `heatNumber`:

• definitionStandard. EN 10168:2004 has no heat-number field: C 00 is "Identification of the sample", and "cast number" appears only in examples. A wrong clause is worse than none.
• legalBasis. Implementing Regulation (EU) 2026/1963 could not be verified.

Checks

• `npm run validate -- --base origin/main`: OK.
• `npm test`: pass, 97.0 % lines.
• `npm run build`: 122 entries; `superseded.json` maps c0872ffd → 2f0d456a.

Closes #128

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