release: prepare QuantumD 0.7.5a0 for production PyPI

[WindDAnalytics]

Purpose

Prepare QuantumD 0.7.5a0 for its first production PyPI release.

Primary experience

python -m pip install quantumd
quantumd quickstart my-first-quantumd-project

A manually managed virtual environment is optional. pipx and uv tool
paths are documented for protected system Python installations.

Supply-chain controls

• production PyPI Trusted Publishing through GitHub OIDC
• exact authorized workflow .github/workflows/publish-pypi.yml
• protected GitHub environment pypi
• separated build and publish jobs
• no stored PyPI password or long-lived API token
• tag/version contract, source tests, wheel inspection, isolated installation,
  fail-closed validation, and KMS-attested release demonstration

Release trigger

Merging this PR does not publish. Publishing occurs only when the deliberate
v0.7.5-alpha tag is pushed after merge.