Standardize release notes: always significant-change highlights, never a size-based trim

[Marcogn]

Summary

This replaces the existing 40-line cutoff (a short section used verbatim, a long one abridged to headings-only) with one uniform rule, applied the same way across 3DSAppManager, CoverDex, and ThePatientGamerHelper's release.yml:

• The GitHub Release body is now always just this project's ### <Type>: <summary> heading bullets from CHANGELOG.md's matching section — never the full section text, and never gated by a line-count judgment call.
• CLAUDE.md's "Changelog policy" section now spells out why the heading convention matters beyond readability: the release workflow publishes those heading lines verbatim as the Release body, so a sloppy heading ships straight to the Release page as-is.
• A section with no ### headings at all falls back to publishing the whole section as-is instead — a structural fallback for a section with nothing to extract, not a size cutoff.
• The release notes always end with a link back to CHANGELOG.md's matching dated section, via GitHub's real heading-anchor slug algorithm (unchanged from before).
• Replaced the in-progress ## Unreleased entry describing the old 40-line behavior with one describing this change instead, since the old entry was describing behavior that never shipped in a release.

Supersedes #18, which proposed the same idea but left the actual extraction gated behind the 40-line threshold (and its own CHANGELOG.md description was inconsistent with its code, describing a 1500-character cutoff that wasn't what the code did) — closing that PR in favor of this unconditional approach, applied uniformly with the other two repos.

Test plan

• python3 -c "import yaml; yaml.safe_load(open('.github/workflows/release.yml'))" — YAML parses.
• Ran the heading-extraction logic standalone against a simulated multi-section entry (### Fix:/### Changed:/### Removed: headings with prose+bullets underneath) — correctly collapses to just the three heading lines, ignoring the bullets under them.
• make test not re-run in this pass — this change only touches .github/workflows/release.yml, CLAUDE.md, and CHANGELOG.md, none of which affect source/.
• Not run end-to-end via an actual workflow_dispatch (would cut a real release, and the real build requires devkitARM which isn't available in this sandbox).

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