release: prepare 0.76.0

[msaad00]

What changed

This is the 0.76.0 release-prep PR.

It aligns the final public release surfaces after the recent graph, AST/SAST, PDF export, container layer attribution, and docs polish waves:

• bumps package, registry, Docker, Helm, and docs references to 0.76.0
• refreshes generated product metrics and lock metadata
• updates the short product description across package and registry surfaces
• aligns release-managed docs, examples, tests, and metadata with the current shipped product state
• adds the 0.76.0 changelog entry

Why

The product work is already on main. This PR makes the release surfaces truthful and internally consistent before tagging and publishing.

Impact

• PyPI, MCP registry, Docker, Helm, docs, and site metadata all describe the same 0.76.0 product
• release examples and tests no longer carry stale 0.75.15 references
• the public one-line description is stronger and less underpowered

Validation

• python -m pytest -q tests/test_deployment_probe.py tests/test_graph_wave23.py tests/test_rate_limit_headers.py tests/test_pdf_output.py tests/test_cli_scan.py tests/test_core.py tests/test_auto_update_db.py tests/test_oci_parser.py tests/test_output_cov.py
• git diff --check
• commit hooks passed: ruff, ruff-format, mypy, bandit, YAML/JSON/TOML checks

Notes

• One historical fixture in tests/test_sbom_ingestion.py intentionally still references 0.75.15 as an older input version example.
• The demo GIF asset can still be regenerated later, but that is not required for the version bump.