mountSlackTag: forward botToken to wireBot so Block Kit replies actually work

[TheGreatAxios]

Summary

• wireBot's WireOptions.botToken (added in Reconcile TagThread.post(): convertMarkdown opt-out + Block Kit blocks/unfurl suppression #6 for the Block Kit reply path) was never threaded through from mountSlackTag, the package's actual entry point — mountSlackTag spreads MountSlackTagOptions (which has no top-level botToken, only slack.botToken) into wireBot(), so WireOptions.botToken stayed undefined for any host using the mount instead of calling wireBot directly.
• Net effect before this fix: TagThread.post(text, { blocks }) silently degraded to plain-text-only for every real deployment (the documented "no bot token" fallback), even with a bot token configured.
• Fix forwards the same token the Slack adapter itself authenticates with, mirroring the existing userLookup auto-wire one line above it.

Test plan

• CI: bun run typecheck && bun run test
• No new test: the passthrough is a one-line, unconditional forward with no branching logic of its own (the actual blocks/unfurl behavior it enables is already covered by wireBot's own test suite via a direct botToken option). mountSlackTag isn't practically unit-testable without a real Chat instance, matching this file's existing test coverage boundary (see index.test.ts).
• Not run locally (sandboxed dev machine); tests will run in this repo's CI.