Implements the identity layer of gogobee_subclass_system.md: 15 subclasses
(3 per class) selectable at L5 via !subclass.
- Schema: new subclass + last_subclass_respec_at columns on dnd_character.
- Registry (dnd_subclass.go): 15 entries with class, display, tagline, and
TwinBee flavor line; helpers for prompt rendering and input resolution
(number, id, or display-name; case/space/hyphen-insensitive).
- !subclass command: bare form prints prompt or current; !subclass <name>
selects (free first time) or changes (500 euros + 30-day cooldown via
separate timestamp from the full !respec wipe). Save-then-debit ordering
mirrors !respec audit fix B.
- Level-up DM at L5+ now embeds the real selection prompt instead of the
Phase 9 placeholder; suppressed once a subclass is set.
- Sheet shows the subclass below the class line, or nudges !subclass when
unchosen at L5+.
- Existing !respec full-wipe also clears subclass + cooldown timestamp.
Mechanical effects of L5/7/10/15 subclass abilities deferred to SUB2/SUB3.
