fix(docs): install phenology extra during docs build

[ryanpavlick]

Docs deploy after v1.10.1 release failed with:

WARNING: Failed guarded type import with ModuleNotFoundError("No module named 'xarray'")
WARNING: Cannot resolve forward reference in type annotations of "hyplan.phenology.fetch_phenology_spatial": name 'xr' is not defined

docs.yml runs Sphinx with -W (treat warnings as errors) and only installed the docs extra. hyplan.phenology imports xarray under a TYPE_CHECKING guard for its annotations, so without xarray the forward-reference warning fires. Adding phenology to the docs install resolves both warnings.

Note: PR-tier CI didn't catch this because docs.yml only triggers on push-to-main, not pull_request. Triggering on PRs is a follow-up improvement.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.76%. Comparing base (b598751) to head (ffeb892).
⚠️ Report is 1 commits behind head on main.
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Additional details and impacted files

@@           Coverage Diff           @@
##             main       #9   +/-   ##
=======================================
  Coverage   80.76%   80.76%           
=======================================
  Files          98       98           
  Lines       13924    13924           
=======================================
  Hits        11246    11246           
  Misses       2678     2678           

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