#21904: docs: fix 8 inaccuracies verified against source code

## Summary Fixes 8 documentation inaccuracies found by cross-referencing doc claims against the actual source code. Each change was verified by reading the relevant implementation before updating the doc. - **`concepts/models.md`**: `imageModel` is used for image operations regardless of primary model vision support — not only as a fallback when the primary can't handle images (`image-tool.ts` explicitly documents this intent) - **`concepts/session.md`**: Cron sessions reuse an existing session when still fresh per the configured reset policy; they don't always mint a fresh `sessionId` (`resolveCronSession` in `cron/isolated-agent/session.ts`) - **`concepts/timezone.md`**: Remove "Time format: 12-hour or 24-hour" bullet — `buildTimeSection` in `agents/system-prompt.ts` only emits the timezone line, no format line - **`concepts/agent-workspace.md`**: Qualify the `openclaw doctor` workspace warning as "may warn" — `detectLegacyWorkspaceDirs` currently always returns an empty `legacyDirs` array - **`channels/feishu.md`**: `groupPolicy` default is `"allowlist"` not `"open"` — verified in `extensions/feishu/src/config-schema.ts` (`.default("allowlist")`) - **`channels/slack.md`**: The `groupPolicy="open"` fallback triggers whenever `groupPolicy` is unconfigured (not specifically when `channels.slack` is missing) — verified in `extensions/slack/src/channel.ts` - **`channels/twitch.md`**: Session key format is `twitch:group:<channelName>`, not `twitch:<accountName>` — Twitch monitor dispatches with `peer.kind="group"` and `peer.id=message.channel` - **`cli/directory.md`**: Default output is a formatted table with `ID` and `Name` columns (via `renderTable`), not tab-separated id/name pairs ## Test plan - [ ] Verify rendered docs look correct for each changed file - [ ] Spot-check source references: `src/agents/tools/image-tool.ts`, `src/cron/isolated-agent/session.ts`, `src/agents/system-prompt.ts`, `extensions/feishu/src/config-schema.ts`, `extensions/slack/src/channel.ts`, `extensions/twitch/src/monitor.ts`, `src/cli/directory-cli.ts` 🤖 Generated with [Claude Code](https://claude.com/claude-code)