docs: update the documentation and pin the CI actions

[MAfarrag]

Description

• Updates the documentation to the current API. Every example page still imported the pre-rename Hapi.*
  package and called the old camelCase methods, so nothing in the docs could be copied and run.
• Replaces the meteo-inputs remote-sensing sections, which documented hapi.remotesensing — a module that no
  longer exists — with a pointer to earth2observe, the package that
  now provides the CHIRPS and ECMWF downloads.
• Rewrites Installation.md, which claimed Python 2.7+, an environment.yml that no longer exists, and
  python setup.py install, around the real install paths and a pixi development section.
• Makes mkdocs build --strict pass. The 75 griffe warnings had three separate causes: Returns: continuation
  lines indented at the item level (so each wrapped line was parsed as an extra untyped return), griffe's
  returns_named_value default reading numpy.ndarray: description as a name rather than a type, and about
  fourteen genuinely missing annotations.
• Fixes the docs so they build from a clean checkout: docs/api/distrrm.md and docs/javascripts/mathjax.js
  are required by mkdocs.yml but had never been committed, and check_inputs.PNG was tracked with an
  uppercase extension that only resolves on a case-insensitive filesystem.
• Refreshes the README: removes badges for services that are dead (LGTM, AppVeyor, Read the Docs, Gitter, the
  clone counter) or that pointed at an unrelated project, repoints the rest at serapeum-org, and fixes the
  four image paths, which were root-absolute and therefore broken on GitHub.
• Pins all 17 GitHub Actions references to release commit SHAs and updates GitHub's own actions, which were
  several majors behind.
• Trims the migration-narrative comments from pyproject.toml, keeping only the ones that state something
  non-obvious.

Issues

• Closes docs(examples): update the documentation content to the current API #185 — update the documentation content to the current API
• Closes docs(build): make mkdocs build --strict pass #186 — make mkdocs build --strict pass
• Closes docs(build): fix the files that prevent the docs building from a clean checkout #187 — fix the files that prevent the docs building from a clean checkout
• Closes docs(readme): fix the broken badges and stale instructions #188 — fix the broken README badges and stale instructions
• Closes ci(security): pin every action to a release commit SHA #189 — pin every action to a release commit SHA
• Closes chore(build): trim the migration narrative from pyproject.toml #190 — trim the migration narrative from pyproject.toml

Type of change

Check relevant points.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Built the documentation from the branch worktree, i.e. a clean checkout rather than a developer tree with
  untracked files present: pixi run -e docs mkdocs build --strict completes with no warnings.

• Ran pixi run -e dev mypy, which reports no issues across 22 source files, confirming the added annotations
  did not widen the existing suppression list.

• Cross-checked every image link in docs/ against git ls-files, and fetched every badge URL in the README to
  confirm it renders rather than returning an error state.

• Resolved every pinned action SHA against its upstream repository.

• Test A: pixi run -e docs mkdocs build --strict → clean

• Test B: pixi run -e dev mypy → no issues in 22 source files

Checklist:

• updated version number in pyproject.toml.
• added changes to History.rst.
• updated the latest version in README file.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• documentation are updated.

[sonarqubecloud]

Quality Gate failed

Failed conditions
7.9% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud