Explain priceDisplayLogic field and update existing references

[jopdeklein]

Summary

• Teach the skill about the new priceDisplayLogic input exposed by the Vio MCP (base / base_tax / base_tax_fees / auto, defaulting to base_tax_fees). On the first search the skill now briefly offers to switch modes alongside the initial results, without blocking, and persists the user's choice for the rest of the conversation.
• Replace the old (total) / (per night) suffix with a mandatory (span, inclusion) price label built from the request's priceMode and the response's priceLogic, so every price is clearly tagged as e.g. (total, incl. taxes & fees) — no more guessing whether taxes and fees are in the number.
• Update references/tool-reference.md to document priceDisplayLogic as an input and to correct the priceLogic output enum (now includes base_tax).

Context

Sibling MCP repo introduced priceDisplayLogic across search_hotels, search_hotels_availability, and get_hotels (see openspec/specs/price-display-logic/spec.md). Default is base_tax_fees (fully inclusive), but the field lets callers request pre-tax or room-rate-only totals. The skill needed to (a) know the field exists and surface it to the user just in case, and (b) always label prices with what they actually include — the two prior sources of the "price discrepancy" confusion this story was filed for.

Test plan

• Manual: run a hotel search and verify the skill offers the price-display choice alongside the first results (not before them) and re-runs when the user switches.
• Manual: verify rendered hotel lines carry a (span, inclusion) label for each priceLogic value (base, base_tax, base_tax_fees, base_fees).
• Manual: verify budget phrasing is interpreted as an all-in total unless the user says otherwise.

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