docs(changelog): restore the 0.1.0 heading and file reproducibility fixes under 0.7.3

[spxrogers]

Tidy-up of the two loose ends from the Chocolatey reproducibility work. One of them turned out to be a real bug, not cosmetic; the other I'm recommending against — details below.

✅ Done — CHANGELOG (fixes a regression I introduced)

While poking at this I found that the first reproducible-build changelog edit (in #112) accidentally replaced the ## [0.1.0] — 2026-06-05 version heading with a ### Fixed subsection. The result:

• every 0.1.0 entry (the "first public release" block onward) was left dangling under [Unreleased], so the changelog claimed all of 0.1.0 was unreleased; and
• the two reproducibility notes sat as a stray, duplicate ### Fixed inside [Unreleased].

This PR:

• restores the ## [0.1.0] — 2026-06-05 heading, re-parenting its entries correctly; and
• moves the two reproducibility fixes (the v0.7.1 → v0.7.3 Chocolatey checksum saga) into a proper ## [0.7.3] — 2026-06-20 section.

Structure only — no entry text changed. Result is well-formed and in order: [Unreleased] → [0.7.3] → [0.1.0].

Note: the broader gap (0.2.0–0.7.2 were never written up; [Unreleased] still holds a large backlog of already-shipped features) is pre-existing and out of scope here — it'd need release-by-release archaeology. Happy to tackle that separately if you want it.

🤖 Generated with Claude Code

https://claude.ai/code/session_01CZYQWDcCaPU9tpWxVJz5sF

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