fix: stop showing an update notice on the latest release

[ch4-Zz]

Problem

A release build always advertises an update, naming the version it is already running:

$ ticker --version
ticker version 5.3.0

and the UI shows v5.3.0 available.

Cause

newerVersion compares the raw strings:

if latest != currentVersion {
    return latest
}

• latest comes from the GitHub API tag_name, so it keeps the leading v: v5.3.0.
• currentVersion comes from cmd.Version, injected by .goreleaser.yml with
  -X 'github.com/achannarasappa/ticker/v5/cmd.Version={{.Version}}'. goreleaser expands
  {{.Version}} to the tag stripped of its v, so the binary reports 5.3.0.

"v5.3.0" != "5.3.0" is always true, so every release build shows the notice permanently,
and it survives the 3 hour cache because the cached value is compared the same way.

Reproducible from a released binary's own cache:

$ cat "$LOCALAPPDATA/cache/ticker/update-check.json"
{"checked_at":"2026-08-25T14:41:35+02:00","latest_version":"v5.3.0"}

Fix

Trim the leading v on both sides before comparing. This keeps the existing semantics
(report whenever the strings differ) and touches nothing else:

• Dev builds are unaffected — Check still returns early on "v0.0.0" before reaching
  the comparison.
• A genuinely newer release is still reported.

Why the tests missed it

updater_test.go uses currentVersion = "v5.0.0", with the prefix that release binaries
never have. Added two cases covering a release-shaped current version: one asserting no
notice when only the prefix differs, and one asserting a real update is still reported.

Alternative

If you would rather keep the comparison strict, the equivalent one-line fix is to inject
{{.Tag}} instead of {{.Version}} in .goreleaser.yml, so the binary version matches
both the tag and the v0.0.0 dev default. That changes what ticker --version prints
(v5.3.0 instead of 5.3.0), which is why I went with the updater side here. Happy to
switch if you prefer.

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