Standardise CheckMK variables to the cmk prefix (checkMkUrl -> cmkUrl,
checkmk* -> cmk*) and resolve the ansible/semaphore split by renaming
all booking fields to semaphore*. Includes DB migrations 0001/0002 for
existing databases.
Introduce server-migrations.ts with a named-migration runner that tracks
applied migrations in a _migrations table. runMigrations(db) is called at
startup before routes, so additive schema changes (ALTER TABLE, new settings)
are applied once and skipped on subsequent restarts.
Update ARCHITECTURE.md: five inline edits + new §4.4 documenting the convention.
