docs(wave): add a curated first-wave board of ready issues

[Ayinkx]

What

Adds docs/WAVE_BOARD.md: a curated, single-cycle set of 20 independent status/ready issues for the first Drips Wave, with a bounded budget.

• 6 trivial (600) + 10 medium (1,500) + 4 high (800) = 2,900 points (well within the 25,000/repo program budget).

Why

• Gives reviewers and contributors a concrete, bounded first-Wave scope instead of the full 116-issue backlog.
• Deliberately excludes status/blocked issues until their dependencies land.

Also applied directly on the repo

• Added the Stellar Wave label (for the Wave label workflow after approval).

Verification

• Every issue in the board is open and carries status/ready.
• Documentation only; no code or CI changed.