docs: end-user README + fix release artifact pipeline

[wavekat-eason]

Summary

• Rewrite the README from an end-user perspective: 3-line Quick Start up top, drop API endpoints from the main command table (moved to a separate API reference section), simplify the sign-in walkthrough from 5 mechanism-heavy steps to 2 sentences, replace the pinned `WK_VERSION=v0.0.3` example with a placeholder, and add a help/feedback section.
• Fix the release artifact pipeline: `release-plz` creates the GitHub release using `GITHUB_TOKEN`, which GitHub suppresses from triggering downstream `release: [published]` events — so `release.yml` never fired and no binaries or `install.sh` got attached to v0.0.1–v0.0.3. Dispatch `release.yml` explicitly via `workflow_dispatch` (which does fire under `GITHUB_TOKEN`) using the tag(s) `release-plz` reports as published.

Note: this PR fixes future releases. v0.0.3 still needs a manual backfill — run `gh workflow run release.yml -f tag=v0.0.3` to attach assets to the existing release so the README's curl|sh URL resolves.

Test plan

• Merge, then verify the next release-plz run dispatches `release.yml` and the new release ends up with all four target tarballs + `install.sh` attached.
• After backfilling v0.0.3 (or the next release), confirm `curl -fsSL https://github.com/wavekat/wavekat-cli/releases/latest/download/install.sh | sh` works end-to-end.
• Render the README on GitHub and sanity-check the Quick Start, table, and section anchors.

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