[TypeSpec to SDK Release] Auto-abandon release plans in early stage and miss target release month

Of the 15 release plans scheduled for March that are still marked “in progress,” 11 (73%) are actually abandoned. Among these abandoned, 8 were in the early phase (before SDK generation starts) and the left 3 are Swagger-based.

I propose automatically marking a release plan as “abandoned” if it misses its release month while still in the early stage—defined as before SDK generation begins. This reduces noise and helps us focus on releases that are truly in progress.

Start by locating the release-plan status handling and the point where SDK generation begins. Trace how the target release month and early-stage state are represented, then add the automatic abandonment behavior and tests covering missed-month early plans; confirm that later-stage and Swagger-based plans are unaffected.

Written by the indexing model from the issue text.