1.0.0-alpha10: render-tree collector + CwvPanelWeight tightening

Second content release on the alpha7 collector contract. Same
shape as alpha9: implements async-decoration (Shape 2) plus
panel-contribution (Shape 4), opt-in via config, zero overhead
when disabled.

- RenderTreeInstrumentor captures response-level cache metadata:
  tag count, context count, hottest tag prefix.
- RenderTreeCollector ships per-request stats to AsyncContextStore
  at terminate and renders a Render-tree correlation panel
  showing CWV metrics bucketed by tag count.
- BeaconStorage::correlateByRenderTreeSize aggregation buckets
  beacons by tag count (0-25 / 26-100 / 101-300 / 301-1000 / 1001+).

Opt-in via render_tree_instrumentation_enabled (default FALSE).
Default installs pay zero overhead. cwv_update_10007 lands the
key on existing installs.

Also tightens CwvPanelWeight constants: adds CORRELATION = 200
midband, bumps TIME_SERIES from 200 to 300, repositions the
correlation panels (per-route, backend cache, render-tree) into
the new band. Fixes the layout discrepancy spotted in alpha9
field testing where AGGREGATION + 100 collided with TIME_SERIES.

CwvPanelWeight constants are due to freeze at beta1; alpha10 is
the last release where they can move.