chore(agents): Expand perf-tuning scope and parallel agent count

- Add `website/server` to investigation target alongside `src`
- Increase parallel agent count from team-based to 10 explicit agents

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yamadashy

.agents/commands/code/perf-tuning.md

@@ -1,13 +1,13 @@
 # Goal
-Improve performance or memory usage of `src` and related code (tests, configs, dependencies) without causing regressions.
+Improve performance or memory usage of `src`, `website/server`, and related code (tests, configs, dependencies) without causing regressions.
 
 Think broadly — algorithm changes, architectural restructuring, parallelization, caching strategies, library replacements, dependency upgrades, and I/O reduction are all fair game. Small logic tweaks that only shave a few milliseconds on a 1000-file run are not worth pursuing. Aim for changes with meaningful, measurable impact.
 
 # Steps
 
 ## Investigation & Planning
 
-Spawn an agent team to investigate efficiently and thoroughly, then form an improvement plan.
+Spawn 10 agents in parallel to investigate efficiently and thoroughly, then form an improvement plan.
 Even if multiple improvements are identified, scope the work to what fits in a single PR — focus on the highest-impact change only.
 
 ## Implementation