Cardano Updates

## Summary

Follow-up to #5261 / #5262 / #5263. The nightly run at
https://github.com/cardano-foundation/cardano-wallet/actions/runs/24722289961
revealed two remaining issues:

1. **Default `success()` filter poisons the downstream chain.** When
`e2e-linux` / `e2e-windows` are skipped on nightly, the default
success() filter on jobs without an explicit `if:` treats the transitive
skip as non-success and skips them too. `verify-assets`,
`publish-release`, `push-docker` and `update-docs` were all skipped on
the nightly run even though `create-release` succeeded. (`push-docker`
has actually been skipped on every prior nightly for the same reason —
pre-existing.)
2. **Nightly asset filenames embed the release-version (date), not the
tag.** `gh release upload file#label` only sets the display label; the
real asset name stays as the source filename. So on nightly,
`cardano-wallet-v2026-04-21-linux64.tar.gz` is the real asset and
`cardano-wallet-nightly-linux64.tar.gz` is only a label. The new
`verify-release.yml` was downloading by
`cardano-wallet-\${TAG}-linux64.tar.gz` which would not match for
nightly.

## Changes

- `release.yml` — add `if: \${{ !cancelled() && needs.<upstream>.result
== 'success' }}` to `verify-assets`, `publish-release`, `push-docker`,
`update-docs`.
- `verify-release.yml` — linux/macos/windows download patterns use
`\$EXPECTED` (release-version) instead of `\$TAG`. Docker stays on
`\$TAG` since the docker asset is renamed by tag at upload time.

## Test plan

- [ ] Dispatch `release.yml` nightly against this branch
- [ ] Verify the four post-create-release jobs actually run
- [ ] Nightly release un-drafts after `publish-release`
- [ ] Docker image pushed to Docker Hub under `nightly` tag

Default success() filter skips jobs whose transitive ancestors
(e2e-linux, e2e-windows) are skipped on nightly runs, breaking the
post-create-release chain. Add explicit !cancelled() + needs-result
guards so verify-assets, publish-release, push-docker and update-docs
run when their direct prerequisites succeed.

Also fix verify-release.yml: nightly asset filenames embed the
release-version (date), not the tag, so download patterns must use
$EXPECTED not $TAG for linux/macos/windows assets. Docker asset is
renamed by tag at upload time and stays on $TAG.

Second hotfix for #5265. `lib` in flake.nix is the custom `nix/lib.nix`
which only re-exports a subset of `nixpkgs.lib` — `splitString` isn't
among them, so my first hotfix #5267 (`builtins.splitString` →
`lib.splitString`) was equally broken.

Switch to `builtins.match` with a regex so we don't depend on the host
lib's re-exports. The regex also tolerates the `0.` prefix present in
`(builtins.head exes).version` since the cabal file reads `version:
0.2026.4.17`.

## Test plan
- [x] `nix eval` returns `v2026-04-17` for both `0.2026.4.17` and
`2026.4.17`
- [ ] Nightly `Build Docker Image` passes

The custom nix/lib.nix only re-exports a subset of nixpkgs.lib — not
`splitString` — so `lib.splitString` was still missing. Switch to
`builtins.match` with a regex that also tolerates the `0.` prefix
that haskell.nix includes in `.version` (cabal file says
`version: 0.2026.4.17`).

Hotfix for #5265 — `builtins.splitString` doesn't exist (it's in `lib`).
Broke `Build Docker Image` on the nightly immediately after #5265
landed.

## Test plan
- [x] `nix eval` with `lib.splitString` returns `v2026-04-17` for cabal
version `2026.4.17`
- [ ] Nightly `Build Docker Image` job passes

builtins.splitString doesn't exist; splitString lives in lib. This
broke the Build Docker Image job on the nightly right after #5265
landed.

Merge the release-candidate branch back to master after the v2026-04-17
release.

The release pipeline's cabal-version-drift guard fired on the next
nightly because master still has cabal version \`2026.4.3\` while the
last release tagged \`v2026-04-17\` (cabal \`2026.4.17\`). This PR
brings the 4 version-bump commits back into master so the next
release/nightly can proceed.

- swagger.yaml wallet version
- *.cabal cardano-wallet version
- README.md wallet/node tags
- run/common/docker/run.sh RELEASE_WALLET_TAG

## Test plan
- [ ] Nightly release workflow runs past \`Prepare Release Candidate\`
without cabal drift error.