ci(release): make winget job bootstrap-aware for un-submitted manifest (#484)

[padak]

What

Make the winget job in release-kbagent.yml bootstrap-aware: distinguish the known, expected "package not yet submitted to microsoft/winget-pkgs" state from a genuine wingetcreate failure.

• On a "was not found" result (the package has no initial manifest yet), the job now skips with a loud ::warning:: and a $GITHUB_STEP_SUMMARY entry pointing to winget: first-ever release run fails — package was never bootstrapped in microsoft/winget-pkgs #484, and exits 0.
• Any other non-zero result still hard-fails the job (::error:: + original exit code).

Why

Per #484, v0.66.1 was the first release ever to actually reach the winget job (previously skipped because its needs: chain failed until #476). wingetcreate update only patches an existing manifest — and Keboola.KeboolaCLI2 has never been bootstrapped in microsoft/winget-pkgs. So the job 404s with was not found and fails, even though the WinGet channel being absent is the same expected state as every prior version.

This change stops that expected, un-bootstrapped state from masquerading as a silent regression in the release run, while keeping real winget errors fatal.

Scope / what this does NOT do

This is only issue #484's optional follow-up (point 3). It does not perform the actual first-time submission — that still requires a human with WINGET_TOKEN access to run wingetcreate new locally/interactively once against the Windows asset and shepherd the initial PR through Microsoft's review, as described in the issue. Once that initial manifest is merged upstream, wingetcreate update succeeds normally and this skip branch is never taken.

Testing

• python3 -c "import yaml; yaml.safe_load(...)" — workflow YAML parses.
• Reviewed the bash branch logic: set +e / captured $status / set -e, case-insensitive grep -qi "was not found" for the skip path, hard-fail preserved for every other exit code.
• Pure CI workflow change — no CLI/Python surface, no changelog entry required (make changelog-check passes), no silent-drift command surfaces affected.

Note for review: this deliberately makes the un-bootstrapped winget state non-fatal. If the release pipeline should instead keep hard-failing until bootstrap, that's a one-line change (drop the exit 0).

Fixes #484