ops/tooling: hosted faucet service for public testnet

[TheNewAutonomy]

Goal

Provide a safe way for wallets/users to request testnet funds without embedding a shared faucet private key in clients.

Scope

• Minimal HTTP service that signs/submits a faucet transfer tx
• Rate limiting / allowlist / captcha hooks
• Wallet integration guidance (request -> tx_id -> receipt tracking)
• Operational guidance (key storage, rotation, monitoring)

Acceptance criteria

• Wallet can request funds and reliably receive a tx_id
• Faucet service prevents trivial draining/spam

[TheNewAutonomy]

Adding concrete sub-issues for the hosted faucet workstream:

• faucet: top-up + key custody strategy for public testnet #233 faucet top-up + custody strategy (low-balance alerts, replenishment runbook)
• faucet: public web app + abuse controls (rate limits, eligibility) #234 faucet public web app + abuse controls (rate limits/eligibility)

(Once mainnet exists, eligibility can be tied to holding real tokens.)

[TheNewAutonomy]

Implemented public-testnet-safe faucet genesis options.

• Added protocol config:
  • faucet_mode: deterministic | configured | disabled
  • allow_deterministic_faucet: must be true to use built-in [0xFA;32] faucet
  • faucet_pubkey_hex + faucet_balance for configured treasury prefund
• Genesis hash now binds to faucet pubkey/balance in the descriptor.
• Updated docs to clearly separate local/dev convenience vs public testnet.

Commit: c5c4310 (pushed to tna_testnet).