feat: complete the Action bootstrap flow

[attomus-gh]

Summary

• generate X25519 and Ed25519 identity material, a signed pre-key, and 100 one-time pre-keys in the runner
• register the public bundle through the ADR-0166 bootstrap endpoint
• seal the complete private device state with the repository secret-storage public key and write SEMAFORE_DEVICE_KEY
• refuse existing device-secret overwrite and avoid retrying the one-time registration request
• replace the bootstrap scaffold status and setup example with the working flow

GitHub token requirement

The built-in GITHUB_TOKEN cannot receive repository Secrets permission. Bootstrap therefore requires an explicit fine-grained PAT or GitHub App installation token scoped to the target repository with Secrets: write. The README instructs operators to revoke the temporary token and delete its repository secret after bootstrap.

Tests

• server bootstrap request validates against the byte-identical sf-server contract schema
• generated public and private key material is cross-checked, including Ed25519 signature verification
• GitHub sealed-box ciphertext is decrypted in-test to prove the stored value round-trips
• existing-secret refusal, GitHub auth failure, malformed public-key response, post-registration write failure, secret-size bound, and one-shot no-retry behavior are covered

Verification

• npm ci
• npm run verify: 6 files and 23 tests pass; audit reports 0 vulnerabilities
• NODE_ENV=test node import of the committed bundle
• actionlint over repository workflows
• action metadata YAML parse
• gitleaks detect --no-banner -v --redact: no leaks
• git diff --check

Harness and release gate

No sf-test-harness executable change is included. The Action tests exercise the exact server contract and real crypto locally; a real staging bootstrap, notify delivery, and execute run remain required before the Marketplace release. This PR does not claim staging proof.