feat!: rebrand SDK to glassflow-rius, import rius

[PabloPardoGarcia]

Implements GLA2-322 per the naming decision recorded on the ticket: pip install glassflow-rius, import rius (repo already renamed to rius-sdk-python; GitHub redirects old URLs).

What changed

• src/glassflow → src/rius (git renames); all imports, docstrings, tests, README, CLAUDE.md follow. Full suite green (ruff, format, mypy strict, 171 tests) and uv build produces glassflow_rius-* artifacts.
• pyproject.toml dist name, keywords, repo URLs; release-please package-name and version-file path.
• DEFAULT_ENDPOINT → https://ingest.eu.console.rius-glassflow.com (GLA2-311 production host) — closes the long-flagged docs/SDK endpoint mismatch.
• telemetry.distro.name resource attribute → glassflow-rius.

Deliberately unchanged (wire/config contracts, tracked on the ticket)

• GLASSFLOW_* environment variables.
• The glassflow OTel tracer scope name (backend keys on it; now guarded by a comment).
• The glassflow.span.pending marker attribute.
• No compat shim for import glassflow: pre-launch, no external users; internal consumers (argus-canary) get a pin+import update once the first release ships.

Manual steps after merge (cannot be scripted)

1. PyPI Trusted Publishing must be configured for the new project name glassflow-rius against rius-sdk-python before the release workflow can publish.
2. The release-please PR this triggers will be the first glassflow-rius release (breaking → 0.8.0 under bump-minor-pre-major).
3. Docs update is held per parallel work in the docs repo — it needs the new name in scripts/requirements.txt + every code sample, and can only pin after step 2 publishes.

BREAKING CHANGE: install glassflow-rius instead of glassflow-ai; import rius instead of import glassflow.