feat(isac): add weapon mod data management

docs/architecture.md

@@ -233,6 +233,34 @@ talent effects use `base × (1 + upgrades / 5)` for zero to five upgrades.
 Server actions validate all relationships and append the full owned graph to
 the existing `game_data` audit history.
 
+### Weapon Mods and tiered weapon slots
+
+`weapon_mod_slots` records each weapon's available slot vocabulary per tier.
+Canonical validation requires four unique slots for T0 and five for T1/T2 for
+every tier at or above the weapon's native tier. Regular Weapon Mods declare a
+single slot type and one or more compatible base weapon categories through
+`weapon_mod_compatible_categories`; eligibility requires both a category match
+and the slot to exist on the equipped weapon at its selected tier.
+
+Exotic Weapon Mods instead reference one `exotic_weapon_id`. They do not carry
+regular category compatibility, are considered permanently equipped, and may
+only be leveled. They do not use quality profiles, random primary rolls,
+secondary pools, or regular Mod Effects. Their canonical contributions are
+fixed attribute references with explicit level-1 and level-20 values in
+`weapon_mod_exotic_attributes`; intermediate values interpolate linearly.
+
+All regular Weapon Mods permit Firepower, Toughness, or Engineering as a
+builder-time primary choice. `weapon_mod_quality_values` stores the shared
+level-1 and level-20 primary roll endpoints for each quality; primary values
+interpolate linearly from levels 1–20.
+
+`weapon_mod_secondary_options` is the shared pool from which a build selects
+two distinct secondary attributes. Every option owns a minimum and maximum at
+each quality through `weapon_mod_secondary_quality_values`; secondary
+availability is not tied to a numbered slot in canonical data. Mod Effects are
+triggerless, hold one or two attribute references, and store fixed per-quality
+values in `weapon_mod_effect_quality_values`.
+
 # Skill Chip quality scaling
 
 Skill Chip sets support Superior and High-end chip instances. Each set owns one