feat: add firecrawl_packs for Alexandria provider context

[rakshith48]

Adds firecrawl_packs, a free, read-only source of agent-facing context for fantasy football and marketing research. Users ask normally; packs help the assistant choose providers and use their data accurately. They do not run workflows or require an intake questionnaire.

• {} lists pack summaries and a nextTool to load each one.
• {"pack":"fantasy"} or {"pack":"marketing"} returns provider IDs, compact purpose summaries, representative capability IDs, a short skill and two illustrative examples. There is no task parameter or recipe selection.
• Provider nextTool calls browse compact live capabilities through firecrawl_find_tools with includeCosts: true. Inspect selected contracts before execution through firecrawl_scrape; the pack does not embed full contracts or frozen prices.
• Guidance says to reuse supplied information, ask only for materially missing details and choose relevant providers rather than calling them all. It covers scoring differences and league availability, estimates and sourcing, costs and provider terms.

One validated JSON file per pack under src/packs/ supplies the context and discovery wording. scripts/check-packs.mjs checks the representative capability IDs against the live catalogue. Search and find_tools results gain a packs pointer for matching providers only where the tool is registered; the search-only profile is unchanged. Credential requirements match firecrawl_find_tools.

Verified: typecheck and lint; 175/175 tests, including tool shape, removal of the task input, payload budget, keyless parity and discovery pointers. Contract snapshots are regenerated against current main, including #536’s parameter descriptions: use values from the listed provider and capability fields. Pack data, tool inputs and pack behavior are unchanged by the compatibility refreshes. Search retains #546’s API error-message relaying while preserving pack discovery pointers. Actual local MCP outputs are 5,772 characters for fantasy and 5,080 for marketing, each with two examples. All 35 representative capability IDs resolve through live catalogue discovery, and provider handoffs return prices with includeCosts: true.