feat(isac): add gear mod data management

docs/architecture.md

@@ -261,6 +261,26 @@ 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`.
 
+### Gear Mods and tier slot capacity
+
+Gear Mod definitions are standard-quality records only; there is no exotic
+Gear Mod branch. Every definition supplies primary roll ranges for Standard,
+Specialized, Superior, and High-end quality at Levels 1 and 20. Values between
+those endpoints scale linearly. A build instance selects one primary attribute
+from Firepower, Toughness, Engineering, Health, or Armor.
+
+The two secondary slots draw distinct attributes from one shared option pool.
+Each available secondary attribute stores its own minimum and maximum for all
+four qualities. Gear tier determines capacity without per-item configuration:
+T0 gear has one Gear Mod slot, while T1 and T2 gear have two.
+
+Canonical data is stored in `gear_mods`, `gear_mod_quality_values`,
+`gear_mod_secondary_options`, and `gear_mod_secondary_quality_values`.
+Successful mutations use `gear_mod.created`, `gear_mod.updated`,
+`gear_mod.archived`, and `gear_mod.unarchived` audit actions. Contributor
+submissions use the `gearmods` proposal module and remain non-canonical until
+approved by Oversight.
+
 # Skill Chip quality scaling
 
 Skill Chip sets support Superior and High-end chip instances. Each set owns one