Add eve-fit-engine to community resources

[WilliamFalci]

Adds docs/community/eve-fit-engine/ — a Pyfa-parity ship and Upwell-structure fitting calculation engine for JavaScript, published on npm as eve-fit-engine.

Listed as a resource: it is a building block for developers (inject an SDE dataset and a fit, get the derived stat block), not something an end user installs.

Against the listing requirements:

1. EVE related — it computes EVE Online ship and structure fitting stats from the SDE.
2. Developer License — the engine is GPL-3.0-or-later as a derivative work of Pyfa; the bundled SDE snapshot is included by mere aggregation and stays under the EVE Online Developer License Agreement, documented in NOTICE and data/SDE-LICENSE.md.
3. Public — public GitHub repository and public npm package.
4. Production ready — it is the engine behind capsuleers.app's fitting tool, and is validated against Pyfa by a 662-assertion fixture suite plus a differential harness over every published ship (1662/1676 fits match exactly, the residual documented in-repo).
5. Public for at least three months — first published to npm on 2026-06-01.
6. Actively maintained — most recent release 2026-09-12.

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