v4.2.2: sync docs + example compose to wickworks v0.3.x

Wickworks v0.3.0 went primitives-only (removed divergences + the
signals/ package); v0.3.1 made camelCase canonical and tightened
Bar volume validation. mt5-httpapi docs and the example compose
pin were still on the old surface.

- README intro + TA section drop divergences, add primitives-only
  disclaimer; rates/ta body table shows the flat indicators shape
  and marks recentBars inert in wickworks v0.3.x.
- SKILL.md frontmatter + intro + bbands example + full indicator
  catalog rewritten to match wickworks v0.3.x reality (real
  registry names, 8 trader-meaningful categories, divergence row
  removed, missing alt-MAs added).
- docker-compose.yml.example pin bumped v0.2.0 -> v0.3.1 so a
  fresh install no longer ships the pre-purification image.
- Go client RatesTAQuery doc comment fixed (flat indicator shape;
  RecentBars marked inert). No signature change.

No mt5-httpapi runtime code changed.