Reduce Convex plugin rule token usage

The Convex plugin's 18 rules (~100KB) consume a large portion of the context window on every Agent message, especially the 16 rules with `alwaysApply: true`.

Consider either:
- Setting rules to `alwaysApply: false` with `globs: ["convex/**"]` so they only load when working in Convex files, or
- Moving longer procedural rules into skills (on-demand) instead of always-on rules

This would reduce token usage for chats that aren't Convex-related while still guiding the agent when needed.

Locate the Convex plugin's 18 rule files and inspect their alwaysApply and globs settings, along with any existing skills. Compare which rules load for Convex and non-Convex work, then choose the approach that preserves guidance for Convex files while reducing unrelated context usage. Done means non-Convex messages no longer load the full rule set and Convex work remains covered.

Written by the indexing model from the issue text.