[Bikebrainz]

repeater set read request files through Bash command substitution, which removed NUL bytes and trailing newlines. It now transports file/stdin bytes as base64 and loads them through the same reversible editor mapping as captured requests.

• Reject empty drafts and blank targets before accepting a send, preventing old responses from being reported as a successful no-op.
• Report per-tab response presence correctly and reset stale response metadata when duplicating a request.
• Preserve binary bodies and readable UTF-8 text; empty input clears the request and omitted input preserves it.
• Reject unreadable files, malformed base64 and ambiguous encoding fields before changing the target or draft.
• Preserve the existing text API and normal send settings, including header normalization and automatic Content-Length.
• Update the public changelog, generated roadmap and CLI/API documentation alongside the fix.

Validation

• CLI contract tests cover all 256 byte values, file/stdin input, empty input and unreadable files.
• Real isolated application sends 76,804-byte bodies intact through both file and stdin, plus readable UTF-8 text. Invalid base64 preserves the draft and destination.
• Fresh, completed and duplicated tab response indicators pass against the real app. Empty drafts and blank targets return errors without making a request or printing old response data. Existing history-ID and asynchronous send regressions pass.
• The final local runtime regression passes 64 checks, including strict HTTPS, certificate-cache recovery and native-window startup.
• Local Windows application build, all 102 native suites and all 20 control-responsiveness checks pass; website checks pass (81 Markdown targets, 3 integrity hashes, 117 pages), and the generated roadmap is current.
• All eight cross-platform CI jobs passed on final head 6173ca36d4e88a3a33669bed379424aeab4763a0 (run 36543583792).

Prerequisites #22 and #25 are merged. This PR adds binary file/stdin loading, correct tab response indicators and explicit rejection of empty sends. Response Hex byte fidelity and immediate socket cancellation remain separate roadmap work.