ecosystem: add eltociear Security APIs (tokenguard, skill-audit, contract-guard)

[eltociear]

Adds a Services/Endpoints ecosystem entry for three live, pay-per-call x402 APIs (USDC on Base — no signup, the calling agent's wallet is the auth):

• tokenguard — heuristic ERC-20 rug/safety scan over public RPC (flags mint / blacklist / pausable / tax / upgradeable-proxy / ownership powers a token owner can use) plus wallet-intel and price endpoints. $0.005/call.
• skill-audit — scans AI agent skills, plugins, and prompts for malicious patterns (68-pattern scanner). $0.01/call, $0.03 for fetch-URL-and-audit.
• contract-guard — pre-interaction risk signals for any EVM contract/token address. $0.005/call.

All three return deterministic, machine-readable JSON and are live behind a valid HTTP 402 handshake (Dexter facilitator, 0% fee). Includes an SVG logo.

Supersedes #211, which was accidentally closed when its branch was recreated; this version also adds the logo asset that #211 was missing.

[cb-heimdall]

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