chore: restore 8.7.0-bound work into [Unreleased] after 8.6.2 ships

[ai-cora]

Draft. Companion to #450 (chore/cut-862). Do not merge until after v8.6.2 ships.

After make release 8.6.2 runs, this commit moves the parked content out of ## [Pending 8.7.0] and back into the canonical ## [Unreleased] header, then deletes the temporary [Pending 8.7.0] section.

Branch base & required rebase

This branch is based on chore/cut-862 (pre-release state). It needs a rebase onto post-release master once make release 8.6.2 has pushed the release commit:

git checkout chore/restore-870
git fetch origin
git rebase origin/master

Expected conflict (one hunk, in CHANGELOG.md): the five narrow ### Fixed entries this commit deletes from [Unreleased] will already have been moved into [8.6.2] by release.py's header rewrite. Resolve by accepting the post-release state — those entries belong in [8.6.2] and should not be in [Unreleased].

After resolving, git rebase --continue, force-push the branch, mark the PR ready for review, merge.

What the diff does

• Removes the five narrow ### Fixed entries that lived in [Unreleased] for the 8.6.2 cut (post-rebase: this hunk is the no-op described above).
• Removes the ## [Pending 8.7.0] header line.
• Removes the HTML comment block explaining the temporary layout.

Net effect on post-release master: the content currently under [Pending 8.7.0] becomes the body of [Unreleased], ready to accumulate further 8.7.0 work.

Verification post-rebase

After git rebase origin/master and resolving the one conflict:

• awk '/^## \[/{print}' CHANGELOG.md lists [Unreleased] → [8.6.2] - 2026-05-28 → [8.6.1] - 2026-04-21 → … (no [Pending 8.7.0])
• [Unreleased] contains the Added/Migration/Fixed/Changed/Deprecated/Removed sections from the original pre-cut state.
• [8.6.2] contains only the five narrow Fixed entries.

Sequence

1. Merge chore: park 8.7.0-bound work for narrow 8.6.2 patch release #450 → master.
2. make release 8.6.2 → tag pushes → Actions ship the release.
3. Watch https://github.com/mbailey/voicemode/actions.
4. Rebase this branch per the instructions above.
5. Mark ready for review, merge.