Ember v0.6.0

Added

• ember gui — a native, single-window experiment console for live demos
  (v0.6): an iced app on the tiny-skia software renderer (no GPU or
  webview dependency) with embedded Noto fonts (src/gui_fonts/) for
  offline Latin + Arabic coverage, dark console theme.
• ember web-gui — an offline, single-page browser console for live demos
  (v0.6). A thin presentation layer over the existing v0.5 pipeline: the
  page translates every action into an ember.experiment.v1 specification,
  validates it through the standard RawExperimentSpec::resolve() gate, and
  executes it with the same prepare_run / execute_prepared code as
  ember experiment run. One resident model session serves repeated
  baseline / intervention / restore runs, so the demo loop never reloads the
  model. Bundles are written and self-verified exactly as in v0.5; the
  restore-original leg reports a bit-exact match against the baseline.
  Light/dark theme toggle (defaults to the system preference, persisted in
  localStorage). See docs/v06-gui.md.
• src/gui_native.rs: the native console — same GuiSession core and
  parse_run_request gate as the browser console, runs executed in a
  worker thread so the UI never blocks.
• src/gui.rs + src/gui_page.html: tiny embedded HTTP server (tiny_http,
  localhost only) and a self-contained page (no web framework, no external
  assets) with Arabic/RTL rendering via the browser (dir="auto" per field;
  the UI itself stays LTR).
• cli_experiment::prepare_run / execute_prepared: the v0.5 run path was
  split into a reusable model-load step and an execute step so a loaded
  model can be kept resident. ember experiment run behavior is unchanged
  (it calls both in sequence).