Polish the v2.6 release package

[midwan]

Summary

• include the license and changelog in the v2.6 release archive
• enforce those files and immutable release metadata in package validation
• finalize the v2.6 changelog and refresh the release checklist
• replace implicit AHI data alignment with an explicit directive

Why

The packaged README referenced files that were absent from the archive, and the
v2.6 changelog did not yet cover the host-shell terminal filtering work or link
to the immutable release comparison. The AHI source also emitted an avoidable
auto-alignment warning during otherwise clean release builds.

Impact

Release users receive the complete license and changelog beside the README.
Future release builds fail package validation if the documentation is omitted
or the current changelog comparison does not end at its release tag. The AHI
alignment cleanup changes no generated bytes.

Validation

• docker run --rm -v "$PWD":/work -w /work sacredbanana/amiga-compiler:m68k-amigaos make clean test package
• inspected all 34 files in Host-Tools-2.6.lha
• verified LICENSE and CHANGELOG against their repository sources
• confirmed the warning-free uae.audio SHA-256 matches the pre-change binary:
  0773b8e187d973076b5767b16e38744f9bd5a4b23aabecd2bb9744bfca81b4c5
• git diff --check