Refactor lang_specs to designated initializers with factory pointer

Migrate the lang_specs[] array from implicit positional indexing to
C99 designated initializers ([CBM_LANG_X] = {...}), eliminating a
class of silent ordering bugs when adding new languages.

Changes:
- Add ts_factory function pointer to CBMLangSpec struct
- Convert all 66 entries to designated initializer syntax
- Add _Static_assert guard: array size must match CBM_LANG_COUNT
- Replace 140-line cbm_ts_language() switch with 3-line factory dispatch
- Net reduction: 127 lines removed

This is prerequisite infrastructure for the ~90 new language expansion.

Author: test