[CaffeinatedCoder]

Closes #519 (against release/10.x this closes nothing; the carry of 10.4.0 to main closes it, as #474 did #470)

Problem

This is step 2 of #519. None of the five ## [10.4.0] headings has a date, and the tag goes on the commit that dates them.

Change

Sets ## [10.4.0] — 2026-10-26 in the root changelog and in the four package changelogs. Nothing else changes, because Version is already 10.4.0 (#473).

Tests

• Every sub-issue of Epic: 10.4.0 #472 is closed. The last merges are chore: update the 10.x test projects' packages (#517) #518 (10.x: update the test projects' packages (ASP.NET Core 10.0.14, ComplexIndexes 5.6.0, EF float leg 10.0.14) #517) and fix: reject a string set compared with a value under a collation that may not compare bytes (#512, port of #507) #516 (10.x: reject a string set compared with a value under a collation that may not compare bytes (port of #507) #512), and CI on release/10.x at 07d92df is green.
• CodoMetis.ValueRanges.Conventions.Tests passes locally on this branch (420/420).
• dotnet pack -c Release builds all four packages at 10.4.0, and their release notes open with the 10.4.0 section.
• dotnet run tools/oracles.cs seeds on 07d92df: the result will be posted on Release 10.4.0: date the changelogs, tag v10.4.0, carry the sections to main #519.

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