/office-hours: Surface founder signal reasoning in YC recommendation

The YC recommendation at the end of `/office-hours` uses a three-tier system based on tracked "founder signals" (named specific users, pushed back on premises, demonstrated domain expertise, etc.), but the tier selection reasoning is hidden from the user. The signals and tier are only revealed if the user asks how the decision was made.

**Suggestion:** Include the tracked signals and tier reasoning directly in the recommendation itself. Most founders would appreciate understanding *why* they received a specific message — "we noticed these specific things about how you think" feels earned, while an unexplained intensity gradient feels formulaic. Transparency here strengthens the recommendation rather than weakening it.

**Context:** Discovered during an `/office-hours` session where the founder asked what determines the YC invitation tier.