feat(client): discord.js client + structured READY logging

[mortik]

Summary

• Adds src/env.ts (zod-validated DISCORD_TOKEN / LOG_LEVEL / CONFIG_PATH).
• Adds src/logger.ts (pino, ISO timestamps, configurable level).
• Adds src/client.ts — minimal discord.js Client with just the Guilds intent. Reaction intents (GuildMessageReactions) and the privileged GuildMembers intent will be added in step 5 alongside the actual reaction handlers, so this step doesn't require any Developer Portal changes yet.
• Adds src/events/ready.ts — logs bot tag, connected guilds, and verification count when the gateway fires READY.
• Wires bootstrap into src/index.ts with graceful SIGINT/SIGTERM shutdown.

Implements step 3 of docs/exec-plans/v1.md.

Test plan

• pnpm test — adds 4 env tests on top of the 8 config tests (12 total)
• pnpm lint, pnpm typecheck, pnpm build clean
• Manual smoke (fake token): bootstrap completes, fatal logs cleanly on TokenInvalid
• Manual smoke (real token): connected to FleetYardsNet, READY event logged structured JSON, SIGTERM shut down cleanly

Follow-ups

• Step 4: port the sweep from the original bash script (uses REST, no extra intent needed).
• Step 5: reaction handlers — at that point we'll add GuildMessageReactions + GuildMembers intent + message/channel/reaction partials, and the Server Members Intent toggle in the Developer Portal becomes required.

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