#4215 verify-build upgrade gate silently skips models whose version is a constant

scripts/check_upgrades.ts parseModel reads a model's version with a regex for a literal (version: followed by a quoted CalVer string). A hand-written model that sets version from a constant (agent-sessions/extensions/models/agent_sessions.ts uses a VERSION const, shared with importerVersion) is not parsed, so the gate prints 'No model definitions changed; no upgrade path to check.' and passes. Bumps in swamp-club#4156, #4211 and #4157 were never path-tested. Expected: the gate resolves a same-file const, or fails (not skips) on a changed model file it cannot parse, so a bump is never silently unchecked.