ci(release): fix tag resolution & validation for calendar releases

[jdmartinez]

This PR fixes the release workflow tag parsing and validation.

What it does

• Accepts an optional tag input for workflow_dispatch runs.
• Resolves the tag from the release event (github.event.release.tag_name) or the workflow_dispatch tag input.
• Validates the resolved tag matches YYYY.MM.PATCH (e.g. 2025.11.0).
• Exports TAG into GITHUB_ENV so later steps (pack/publish) use it reliably.

Why

• The previous workflow used ICU-style format strings ({0,number,0000}) inside GitHub expressions which produced FormatException errors on the runner.
• This change replaces that fragile expression with robust shell-based resolution/validation and makes manual runs possible.

Testing & verification

• Local build/tests unchanged; CI should pass.
• To test the workflow:
  • Option A (recommended): create and publish a GitHub Release from tag YYYY.MM.PATCH (e.g. 2025.11.0). The workflow triggers on release: published.
  • Option B (manual run): in Actions → choose Publish Calendar Release → Run workflow → set tag to a valid value (e.g. 2025.11.0).

Notes

• File changed: .github/workflows/nuget.yml (robust tag resolution & validation).
• If you want me to open the PR for you, I can do so once gh is available or via the GitHub web UI (I can also prepare the review checklist).

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Functional	85%	71%	173	✔
Functional.EntityFrameworkCore	100%	100%	8	✔
Summary	86% (224 / 261)	71% (80 / 112)	181	✔

[github-actions]

Test Results

135 tests  ±0   135 ✅ ±0   1s ⏱️ ±0s
  2 suites ±0     0 💤 ±0 
  2 files   ±0     0 ❌ ±0 

Results for commit 3ba901b. ± Comparison against base commit 1c7f4bb.