Add reference links to hardware encoding documentation

[Copilot]

Documentation must include rationale and supporting reference links for all changes. Existing hardware encoding quality improvement docs lacked inline citations.

Changes

Patch file (hwcodec_qp_improvements.patch)

• Added header with rationale and primary references (Sunshine, FFmpeg, vendor docs)
• Added inline // Reference: comments for each code change (9 locations)
• Example:

// Set VBV buffer size for better rate control
// Reference: Sunshine's VBV buffer calculation - https://github.com/LizardByte/Sunshine/blob/master/src/video.cpp#L1746
// Reference: FFmpeg rate control - https://slhck.info/video/2017/03/01/rate-control.html
if (rc_buffer_size > 0) {
  c->rc_buffer_size = rc_buffer_size * 1000;

Integration example (rustdesk_hwcodec_integration_example.rs)

• Added # References section in doc comments for calculate_qp_range() and calculate_rc_buffer_size()
• Added comprehensive References section at file end (15+ links)
• Inline references for each encoder type (NVENC, QSV, AMF, VAAPI, VideoToolbox)

Main documentation (hardware_encoding_quality_improvements.md)

• Converted all QP values to direct GitHub links: min_qp = 19 [(Source)](https://github.com/...#L38)
• Categorized References section: Primary (Sunshine), Hardware vendors, FFmpeg, Technical background
• 27 total reference URLs

Verification document (REFERENCE_COMPLIANCE.md) - NEW

• File-by-file compliance breakdown
• 58+ total reference links cataloged
• Reference quality standards

All technical decisions (QP values, VBV calculations, encoder options) now traceable to authoritative sources.

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