Bug: 'series' taxonomy lookup fails for multi-word names with spaces (e.g., "Some Series Name with Spaces")

[TheGlacius]

Describe the problem:

The series taxonomy, when assigned multi-word names with spaces in post front matter (e.g., series = ['Some Series Name with Spaces']), is not correctly recognized and grouped by the theme's posts/series.html partial.

Steps to reproduce:

1. Ensure series taxonomy is enabled in config.toml.
2. Create at least two (or more) posts that belong to the same series, using a multi-word name with spaces in the front matter.
3. Run Hugo locally.
4. Navigate to one of the single post pages that belongs to the series.

Observed Results:

• What happened?
  The "See also in [Series Name]" section, which is rendered by layouts/partials/posts/series.html, does not appear on the single post page.

• What did you expect to happen?
  I expected a section titled "See also in [Series Name]" (or similar) to appear, listing the other posts in that series, as defined by the series front matter.

Relevant code exceptions or logs

Hugo Version: v0.148.1+extended windows/amd64

When layouts/partials/posts/series.html used the original problematic code (simplified debug output):

DEBUG: Current Page URL: /posts/some-post-in-series/
DEBUG: Series parameters for this page: Some Series Name with Spaces
DEBUG: Raw Series Name from Front Matter: "Some Series Name with Spaces"
DEBUG: Anchorized Name (used for lookup): "some-series-name-with-spaces"
DEBUG: Is $seriesPagesCollection found for slug "some-series-name-with-spaces"? NO
DEBUG: Number of pages in this series collection (some-series-name-with-spaces): 0
DEBUG: Pages in this series (Titles):
DEBUG: CONDITION NOT MET: (len $seriesPagesCollection) > 1 is FALSE. Only 0 pages found.

When a diagnostic debug was added to list all series keys Hugo recognizes ($.Site.Taxonomies.series):

DEBUG: Taxonomy Diagnostic Check
Current Page URL: /posts/some-post-in-series/

DEBUG: Does this page have `series` in its front matter? YES (Value: Some Series Name with Spaces)

DEBUG: All Series Keys Hugo Sees in `$.Site.Taxonomies.series`:
**Key: "some series name with spaces"** (Number of Pages: 2)
- First Post in Some Series
- Second Post in Some Series

Analysis:

The issue appears to be a mismatch between the slug generated by | anchorize (which is some-series-name-with-spaces) and the actual key Hugo uses internally for series taxonomy terms with spaces (which is some series name with spaces - lowercase with spaces).