feat: add search_type to perplexity_search for Fast Search (v1.3.0)

[rbuchmayer-pplx]

Why

Perplexity launched Fast Search on Sep 24: search_type: "fast" on the Search API, lower latency at $1 per 1k requests instead of $5. perplexity_search had no way to request it. perplexity_ask already gets it through the fast preset server-side, so this only touches the search tool.

What

• perplexity_search gains an optional search_type (web | fast). Omitted keeps the API default (web), so existing callers see no change.
• passed straight through in the /search body; tool description and README mention the mode
• version 1.3.0 (package.json, lockfile, server.json, plugin.json, marketplace.json, advertised VERSION)

Verification

Stdio client against the built package and the prod Search API:

server version: 1.3.0
tools/list  perplexity_search.inputSchema.search_type.enum = ["web","fast"]
perplexity_search {query, max_results: 3, search_type: "fast"}  isError=false  290ms  3 results
perplexity_search {query, max_results: 3}                       isError=false  298ms  3 results
perplexity_search {query, search_type: "bogus"}                 -> -32602 input validation error

npm run build, tsc --noEmit, vitest run 90/90.