GOATS-962: Add hidden input fields in observation forms.

[davner]

• Update gpp-client dependency to version 25.10.3.

Checklist

• Added a release note in doc/changes using the PR number.

[Copilot]

Pull Request Overview

This PR adds hidden input fields to observation forms to support form submission requirements while updating the gpp-client dependency to version 25.10.3.

• Added three hidden input fields for observation ID, target ID, and observing mode
• Implemented hidden input handling in the form creation logic with early return to avoid layout disruption
• Updated gpp-client dependency from 25.10.1 to 25.10.3

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

File	Description
src/goats_tom/static/js/gpp/observation_form.js	Added logic to handle hidden input field creation with early return and added explanatory comments for section headers and special field handlers
src/goats_tom/static/js/gpp/fields.js	Added three hidden field configurations for observation ID, target ID, and observing mode in the SHARED_FIELDS array
src/goats_tom/api_views/gpp/observations.py	Added FIXME comment questioning data source for opportunity field
pyproject.toml	Updated gpp-client dependency version from 25.10.1 to 25.10.3

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.36%. Comparing base (3807b94) to head (bf5ee5f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #464   +/-   ##
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  Coverage   78.36%   78.36%           
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  Files         256      256           
  Lines        8164     8164           
  Branches      487      487           
=======================================
  Hits         6398     6398           
  Misses       1677     1677           
  Partials       89       89           

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