docs(wiki): update project wiki

[fro-bot]

Summary

Weekly wiki update since `cf69553`.

Pages updated

• Architecture Overview — Added Discord gateway package (`@fro-bot/gateway`) to the monorepo section with module descriptions; updated services description to note oMo opt-in; updated sources and date
• Execution Lifecycle — Updated `last-updated` date and SHA (bootstrap phase description was updated in a prior dispatch run)
• Setup and Configuration — Updated summary and sources (oMo disabled-by-default content was already added by prior dispatch run `ses_1cb9028baffeaI6dHieKVVvDVS`); updated date
• Index — Updated summaries for Architecture Overview and Setup and Configuration; updated date

Key changes documented

• Discord gateway (`packages/gateway/`): new long-running daemon that bridges Discord `@fro-bot` mentions to agent runs, using Effect for structured concurrency and a mitmproxy sidecar for egress control
• oMo disabled by default: `enable-omo: false` is now the default; oMo plugins are stripped from config in disabled mode

Lint results

• Zero broken wikilinks (the `[[Page Name]]` in index.md is explanatory text)
• Zero orphan pages