chore: prepare v0.10.0-dev

[tobbee]

Reopens development after v0.9.0, restoring the prepare/release pair that was skipped last cycle.

commitVersion = "v0.10.0-dev"  // was v0.9.0
commitDate    = ""             // was the release commit's timestamp

An un-stamped go run now reports a bare go608-clock v0.10.0-dev; Makefile builds are unaffected, since they stamp both from git describe / git log.

Two deliberate choices, both easy to reverse:

• -dev names the release being worked towards, matching v0.8.0-dev, v0.7.0-dev and v0.6.0-dev. It sorts after v0.9.0 and before v0.10.0. This encodes an assumption that the next release is a minor — true for every release so far (0.5 → 0.9, no patch releases). If 0.9.x could be next, v0.9.0+dev presumes nothing, at the cost of breaking the established pattern.
• commitDate goes back to empty. A date belongs to a release, and a development build was not cut from one — leaving v0.9.0's timestamp in place would have every dev build reporting the previous release's date as its own.

Why it matters: version.go reported v0.8.0 for the nine commits between the v0.8.0 release and this cycle, because the v0.9.0-dev opener was never committed. A binary built from main claimed to be a release it was not.

⚠️ Merge order

Based on chore/release-v0.9.0 (#74), so it must land after that PR merges and after v0.9.0 is tagged. Merging this first — or before tagging — would leave the tag pointing at a commit that already says v0.10.0-dev. Until #74 merges, the diff here shows its commit too; afterwards it reduces to the single version.go change.

🤖 Generated with Claude Code

[tobbee]

Rebased on main now that #74 has merged (085d740) and v0.9.0 is tagged. The release commit dropped out as already-applied, so this PR is down to the single version.go change and the merge-order caveat in the description no longer applies — it's ready whenever you are.

Worth noting for the next cycle: v0.9.0 is tagged on the chore(release) commit itself, whereas v0.8.0 landed on a docs commit that followed it. This one is the tidier habit.

🤖 Generated with Claude Code