chore: add copyright headers to keeper, agent, and receipt-cli sources

[emirykl]

Adds the per-file copyright line to all 17 sources listed in the issue.

// Copyright (c) 2026 Sub Rosa contributors

17 files changed, 17 insertions(+), 0 deletions(-) — every added line is the header itself, nothing else is touched.

One deviation, in services/receipt-cli/src/index.ts

The issue asks for the header as the first line of each file. That one file is an executable and starts with a shebang:

#!/usr/bin/env node

A shebang is only honoured on line 1, and TypeScript reports TS18026: '#!' can only be used at the start of a file if anything precedes it. So in that file the header goes on line 2, directly under the shebang:

#!/usr/bin/env node
// Copyright (c) 2026 Sub Rosa contributors
// receipt-cli — export a round receipt from RPC or verify a local file.

This is what license-header tooling does with shebang files generally. Say the word if you would rather the CLI be left out of this change entirely.

Verification

tsc --noEmit against each affected service, all clean:

• services/receipt-cli/tsconfig.json — clean (in particular, no TS18026)
• services/agent/tsconfig.json — clean
• services/keeper/tsconfig.json — clean

Fixes #202