Fixed several small bugs

[TejasMorbagal]

This PR fixes the following:

• osc_themes values are now automatically lowercased, so 'Land' and 'LAND' are treated the same as 'land', preventing theme validation failures.
• collection_id is now validated to contain no spaces; a clear error is raised with a hint to use hyphens instead.
• license_type (dataset) and properties.license (workflow) are now mandatory fields; publishing fails immediately with a descriptive error if either is missing.
• Variable catalog description now falls back to the title-cased variable ID when neither description nor long_name attrs are present on the zarr variable, preventing null description validation failures.
• Pull requests opened by deep-code now include a "Generated with deep-code" note in the PR description.
• stac_catalog_s3_root is now a mandatory field in the dataset config; publishing fails immediately with a descriptive error if it is absent.
• STAC catalog links in the OSC collection now follow the OSC convention: a via link to the STAC browser URL and a child link to the direct HTTPS catalog URL. The s3:// URL is converted to HTTPS (AWS virtual-hosted style) to satisfy the uri-reference format check in the OSC products schema.
• Added optional visualisation_link field to the dataset config; when provided, a visualisation link with title "Dataset visualisation" is added to the generated OSC collection.
• Added optional description field to the dataset config; overrides the description attribute from the Zarr store when set.
• Added optional osc_project_title field to the dataset config to correctly set the project link title (e.g. "DeepESDL") instead of deriving it from the project ID.
• Fixed workflow_id not being normalised (slugified) when stored on Publisher, causing spaces in experiment link hrefs and failing uri-reference format validation

[codecov]

Codecov Report

❌ Patch coverage is 96.63300% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.33%. Comparing base (3e17cca) to head (15ebc76).

Files with missing lines	Patch %	Lines
deep_code/tools/new.py	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #21      +/-   ##
==========================================
+ Coverage   82.63%   88.33%   +5.69%     
==========================================
  Files          24       24              
  Lines        2056     2323     +267     
==========================================
+ Hits         1699     2052     +353     
+ Misses        357      271      -86     

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[TonioF]

Mostly fine, but I have one thing I did not like.

Also, my general understanding is that in non-code text we use British English, i.e., not license but licence. However, this spelling is also used in the OpenScienceCatalogue so we should gho with it.