docs(changelog): prepare 0.7.0 release

[zikolach]

Summary

• promote the current Unreleased changelog entries into the dated 0.7.0
  release section
• add the user-visible mouse routing and parsing fixes from fix(input): address mouse routing review findings #46 to the release
  notes
• update README SBT and Mill install snippets from 0.6.0 to 0.7.0
• update every Scala CLI example to use Maven Central 0.7.0 artifacts and
  remove the mouse demo's local snapshot repository requirement

Validation

• mill --no-server __.compile
• mill --no-server core.test (135/135 passed)
• mill --no-server scalafmtCheck
• mill --no-server scalafixCheck
• openspec validate --all --strict (13 passed, 0 failed)
• git diff --check
• verified all tracked user-facing siglyph dependency coordinates use 0.7.0

Scala CLI published-dependency compilation is intentionally deferred until
after release publication because 0.7.0 is not available on Maven Central
before the release tag is published.