Feature Request: Allow adding custom path to rule-discovery

[medium-effort]

I use both opencode and antigravity IDE (but mainly antigravity). the rules are inside .agents\rules where the IDE automatically injects the frontmatter there into new session and could either use glob or make decision on when to call those optional rule. so would be nice if there's a customizable setting to also add .agents\rules to search for rules.

[frap129]

This is a good idea, but I will have to defer it to the v2 branch (for opencode v2). I dont want to add a standalone config file for a single config option, and opencode v2 supports inline configuration for pluigins.