docs+env accuracy sweep: .env.example and deployment.md contradict the code in eight places

Each item below was verified against source during the CR of #150. None is about that PR's subject; grouping them so one pass can fix them all.

.env.example

• :27 claims the default response model is claude-sonnet-4-20250514; the actual default is claude-sonnet-4-6 (packages/outpost/ai/src/config.ts:21).
• :64 SLACK_BOT_TOKEN=xoxb-... and :65 SLACK_APP_TOKEN=xapp-... are non-empty placeholders. Copying the file satisfies requireEnv (apps/slack-bot/src/config.ts:5-6) and the failure surfaces later as a confusing Slack API error instead of "you did not set the token". Leave the values empty.
• :47 Discord token annotations are swapped: the bot reads DISCORD_TOKEN; DISCORD_BOT_TOKEN is the legacy fallback.
• :134 the Email adapter requires POSTMARK_API_KEY and POSTMARK_FROM_EMAIL (packages/outpost/shared/src/platforms/registry.ts:96-100) and throws without them. Neither is documented.
• Read at runtime but absent from the example: TEAM_MEMBER_IDS (promised by docs/deployment.md:81), ON_CALL_MEMBERS, SYNC_ECHO_WINDOW_MS, SMTP_SECURE.

docs/deployment.md

• :20 instructs every service to point at apps/<app>/railway.toml, but apps/web/railway.toml does not exist — web uses the repo-root railway.toml.
• :79 lists GUILD_ID, which .env.example:54 says was replaced, and omits DISCORD_BOT_TOKEN. See the dedicated issue for that contradiction.
• :173 names the root ESLint config eslint.config.cjs; the repo has .eslintrc.cjs (and ESLint 9 cannot read it — see #141).
• :47 says the five HEALTH_PORT consumers each have "a different fallback", contradicted by the table directly beneath it: teams-bot and worker both fall back to 3003.

Found by: CR rounds 1-2 on #150 (slots 7-1, 4-2, 2-2).

Start by comparing .env.example and docs/deployment.md with the referenced config files: packages/outpost/ai/src/config.ts, apps/slack-bot/src/config.ts, and packages/outpost/shared/src/platforms/registry.ts. Update the eight documented discrepancies, then verify every listed variable, token annotation, Railway path, ESLint filename, and HEALTH_PORT statement matches the code and repository.