feat: add Setup Advisor with Paper Chan optimization guide

Implement auto server setup helper that analyzes server environment,
detects hardware tier, and generates config recommendations based on
Paper Chan's optimization guide (paper-chan.moe/paper-optimization).

New modules :

• setup/detect: platform, hardware, config, and plugin detection
• setup/model: domain models (sessions, proposals, enums)
• setup/rules: 5-rule engine (safety, consistency, conflict,
  fork-specific, performance tuning)
• setup/preset: 3-axis preset matrix (profile × tier × aggressiveness)
• setup/backup: config snapshot/restore with rollback tokens
• setup/report: markdown + YAML report generation

Paper Chan guide coverage:

• Paper world-defaults: redstone-impl, per-player-mob-spawns,
  despawn-ranges, alt-item-despawn-rate, entity-per-chunk-save-limit,
  villager tick-rates, treasure-maps, feature-seeds, and more
• Paper global: chunk-system threads, book validation
• Bukkit: spawn-limits, ticks-per, mob-spawn-range cheat sheet
• Server.properties: allow-flight, pause-when-empty, view/sim distance
• Plugin conflicts: ClearLag, mob stackers, silktouch spawners,
  ETF, anti-Fabric plugins
• JVM: Aikar's flags, ZGC for Java 21+, heap sizing

Modified existing files:

• LessLag.java: wire SetupAdvisor lifecycle
• LagCommand/LagTabCompleter: add /lag setup subcommand
• config.yml: add setup-advisor section
• plugin.yml: add lesslag.setup permission