feat: implement HueCue tracker as OBS Browser Source

[Copilot]

Replaces the WPF→WebSocket→screenshot pattern with a self-contained HTML/CSS/JS overlay that runs natively inside OBS as a Browser Source, eliminating the need for a separate process for in-OBS monitoring.

New: HueCue.BrowserSource/

• obs-source.js — OBS WebSocket v5 client: SHA-256 auth handshake, GetCurrentProgramScene + GetSourceScreenshot capture loop, dispatches obsframe DOM events. All connection params configurable.
• histogram.js — OffscreenCanvas pixel sampling → per-channel histogram → R/G/B line-graph rendering, matching WPF app style.
• overlay.js — Rule-of-thirds grid (canvas lines) and heat-map zone overlay (CSS grid with semi-transparent divs), matching WPF colour palette.
• face-detector.js — MediaPipe BlazeFace via TensorFlow.js CDN; colour-cycled bounding boxes + white keypoints. Degrades gracefully if unavailable.
• index.html — Wires all modules; all settings driven by URL query params. Shows an interactive settings panel when previewed outside OBS (window.obsstudio absent), auto-hidden inside OBS.
• styles.css — Transparent background; histogram panel CSS position variants (right / below).
• README.md — Setup guide, full URL param reference, troubleshooting.

Configuration via URL params (no code changes needed)

file:///…/index.html?obsPort=4455&histogram=right&guide=thirds&faceDetection=true&fps=30&imageQuality=85

Param	Default	Values
obsHost / obsPort / obsPassword	localhost / 4455 / (empty)	connection
histogram	right	right | below | none
guide	none	none | thirds | heatmap
faceDetection	true	true | false
fps	30	1–60
imageQuality	85	1–100

Updated

• docs/OBS-Setup.md — Rewritten: Browser Source is now the primary integration method; WPF app documented as secondary (director/monitoring display use case).
• build_app.yml — Adds a BrowserSource Actions artifact step to bundle the overlay files alongside each release.

Recursive-capture note: placing the Browser Source in the same scene it screenshots will include the previous frame's overlay. Use a dedicated monitoring scene or Studio Mode preview for a clean signal.