Add growthepie API coverage to tools and indexing skills

[mseidlx]

Summary

This PR adds growthepie coverage to the repo so agents have a documented source for Ethereum ecosystem analytics instead of relying on stale assumptions or scraping dashboards.

What changed

• Added growthepie guidance to tools/SKILL.md
• Added growthepie guidance to indexing/SKILL.md
• Surfaced growthepie in the top-level SKILL.md
• Added discoverability updates in README.md
• Documented fees/table.json as the shortcut for latest hourly transaction-fee data across covered chains

Endpoints documented

• master.json
• fundamentals.json
• export/{metric}.json
• fees/table.json
• chains/{origin_key}/overview.json
• metrics/chains/{origin_key}/{metric_id}.json
• labels/projects.json
• labels/projects_filtered.json
• apps/details/{owner_project}.json

Notes

• fees/table.json is documented as chain-keyed hourly data under chain_data
• project label endpoints are documented as table-shaped payloads with types plus row arrays
• guidance includes rate-limit and coverage caveats from the live docs/API

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