v0.2.2: passive update-availability nudge

[sbroenne]

Summary

Adds a passive update-availability nudge (the DIY option, notify-only — no self-swap of the binary). Ships as v0.2.2.

When adomd runs interactively, it does a best-effort check against the GitHub Releases API and, if a newer release exists, prints a single line to stderr:

adomd: version 0.2.3 is available (you have 0.2.2). https://github.com/sbroenne/adomd-cli/releases/tag/v0.2.3
adomd: set ADOMD_NO_UPDATE_CHECK=1 to silence this check.

Design guarantees

• Never touches stdout — JSON output is unaffected.
• Throttled to at most one network call per day; result cached in %LocalAppData%\adomd-cli\update-check.json.
• Fast/safe — 2s HTTP timeout, every failure swallowed (offline, rate-limited, etc.).
• Automation-friendly — auto-suppressed when stderr is redirected (scripts/CI), and hard opt-out via ADOMD_NO_UPDATE_CHECK=1.
• No binary swapping — it only tells you; you download and replace adomd.exe yourself. Reuses the existing GitHub Releases + SHA256 infrastructure.

Tests

• 72 tests total (+10). New coverage: tag parsing (v-prefix, pre-release/build metadata stripping), version comparison, and the opt-out/redirect gating logic.

Verification

• Build clean, dotnet format clean, 72/72 tests pass.
• Confirmed the live GitHub API returns a parseable tag (v0.2.1) and that probe stdout stays clean, parseable JSON with the notifier wired in.
• Note: the stderr line is intentionally suppressed when stderr is redirected, so it doesn't appear in captured/CI output by design — the gating and parse/compare logic are covered by unit tests instead.

Co-authored-by: Copilot App 223556219+Copilot@users.noreply.github.com