#23056: fix(slack): exclude archived channels from startup channel resolution

## Summary `listSlackChannels()` in `resolve-channels.ts` calls `conversations.list` with `exclude_archived: false`, which paginates through **every** channel in the workspace including archived ones. For workspaces with thousands of archived channels (e.g., a 10-year-old Slack install), this: - Burns through Slack's rate limit on every gateway startup - Causes `rate_limit_exceeded` warnings with 30-second retry delays - Compounds when the gateway restarts multiple times (each restart re-fetches the full list) ## Fix One-line change: `exclude_archived: false` → `exclude_archived: true` This is safe because `resolveByName()` already prefers active channels over archived ones (line 89), and channels referenced by ID don't need the list at all — they're matched directly. Supersedes #19870 (closed due to stale branch). ## Test plan - [x] Verified channel resolution still works when channels are referenced by ID (e.g., `C02LFRN0V`) - [ ] CI passes 🤖 Generated with [Claude Code](https://claude.com/claude-code) <!-- greptile_comment --> <h3>Greptile Summary</h3> Changed `exclude_archived` from `false` to `true` in `listSlackChannels()` to prevent fetching thousands of archived channels during gateway startup, avoiding Slack API rate limits. - Resolves rate limit warnings for workspaces with large numbers of archived channels - Name-based resolution already prefers active channels (resolve-channels.ts:89) - ID-based channel references continue to work (resolved as `true` even if channel metadata is missing from the list) - The `archived` field is only used for logging, so missing metadata for archived channels referenced by ID has no functional impact <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - Simple one-line fix that addresses a real performance issue without breaking existing functionality. The change is well-justified and the code already handles the edge case where archived channels might be referenced by ID - No files require special attention _{Last reviewed commit: 7c4858b} <!-- greptile_other_comments_section --> _{(5/5) You can turn off certain types of comments like style [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->