Index C# namespace declarations as modules

[odvcencio]

Adds a narrow supplemental C# tags query so simple and qualified namespace declarations appear as module definitions without replacing inferred tags.

Evidence:

• Python decorated declarations were rejected as already indexed.
• Exact C# baseline preserves five enclosed symbols but omits both namespace containers.
• Feature focused regression passes 20 consecutive runs.
• Accumulated eight-language tag matrix passes.
• Treesitter package, full repository, and full race suites pass.
• Exact live CLI index changes from five symbols to seven with Acme.Telemetry and Utilities module definitions.
• Changed-file and commit-range secret scans report no findings.