PDK 0.4.0

Added

• Integrator best practices for bindings and performance (BP001-BP018): tag() in bindings, script transforms
  that should be map or expression transforms or that block, binding loops and mirrored bidirectional bindings,
  change scripts without an origin guard, bound input params, fast polling, clocks and runScript, pass-through
  expressions, a tag bound many times, UDTs dropped by binding, deep embedded views, queries and heavy components in
  repeated views, literal colors, repeated inline styles, bindings that move the layout. Errors and warnings only
  for what breaks or costs; the rest is information.
• pdk refs tag|view and the pdk_refs MCP tool: where a tag or a view is used in a project, with indirect tag
  paths expanded through the params the view's callers pass. pdk inventory (Markdown, CSV, JSON): every view
  with its routes, params, callers, tags and write points, named queries, and the views nothing opens.
• pdk validate --tags (tags=true in pdk_validate, and on every deploy as warnings): tag paths checked on the
  gateway, indirect ones expanded through the callers. New codes R020 (tag not found) and R021 (paths known only
  at runtime).
• The eyes open views promoted to the target: pdk inspect work/<target>/<view> adds a /pdk/ preview page to the
  target's page configuration, the only change the module accepts there; promote --to-project says how to look.

---

Suggested from the changes since v0.3.0: v0.4.0. Publishing this draft releases it: it tags
main, attaches the wheel, publishes to PyPI and moves these notes under [0.4.0] in CHANGELOG.md.
To release another version, change the tag before publishing (vX.Y.Z).