Update documentation to 26.1 LTS

[MichaelFisher1997]

Changes:

• Set version to 26.1
• Remove unstable warning banner
• Clean version selector to show only 26.1

Testing:
Please test on Cloudflare preview before merging to ensure it deploys correctly.

Summary by CodeRabbit

• Chores
  • Updated documentation version configuration to reflect version 26.1 as the current release.
  • Added Nix flake configuration to establish a standardized development and documentation build environment.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR updates the documentation configuration to version 26.1 and adds a Nix flake configuration file for managing the development environment. It marks version 26.1 as the current stable release and defines Python 3.11 development shells with Sphinx and related documentation packages.

Changes

Cohort / File(s)	Summary
Configuration Version Update conf.py	Updated version identifiers: godot_version changed to "26.1", godot_is_latest set to False, and godot_versions now contains only the 26.1 release with root path mapping.
Development Environment Setup flake.nix	Added Nix flake configuration with multi-system support. Defines devShells.default for interactive development with Sphinx and documentation tools, and apps.default that provides a build-docs app wrapper executing the repository's build.sh script.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• Add Redot 26.1 LTS documentation branch #142: Directly related version configuration update to 26.1 in documentation settings.
• Add automated documentation build workflow for 26.1 LTS #143: Related configuration changes to godot_version and godot_versions in conf.py affecting release selection.

Suggested reviewers

• Arctis-Fireblight

Poem

🐰 A version twenty-six, now set in stone,
With Nix and Sphinx to help it grown,
The docs now build with flake so true,
Where dev shells bloom the whole year through! 🌿

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Update documentation to 26.1 LTS' directly matches the main objective of the pull request and accurately describes the primary changes in conf.py.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 1

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

conf.py (1)

210-211: ⚠️ Potential issue | 🟡 Minor

Pre-existing bug: html_extra_path is overwritten — robots.txt is silently dropped.

Line 211 reassigns html_extra_path, discarding the robots.txt entry from Line 210. This isn't introduced by this PR, but since you're touching conf.py, it's worth fixing:

Proposed fix

-html_extra_path = ["robots.txt"]
-html_extra_path = ["sitemap.xml"]
+html_extra_path = ["robots.txt", "sitemap.xml"]

🤖 Fix all issues with AI agents

In `@flake.nix`:
- Around line 48-57: The app program uses cd ${self} which points to a read-only
Nix store path and will fail when build.sh writes output; update the program
(the pkgs.writeShellScript block under apps.default / program) to run in a
writable location (e.g., remove cd ${self} and operate from the current working
directory or create a temporary work dir) and include the missing runtime tools
by adding pkgs.gnumake, pkgs.parallel, pkgs.libwebp, and pkgs.imagemagick to the
PATH (or reference their bin directories) alongside pythonEnv and pkgs.git so
build.sh has the required executables available. Ensure the script uses a
writable path before invoking FULL_RUN=1 ./build.sh and that PATH includes the
added packages.

[MichaelFisher1997]

Closing this PR. Will create a new one targeting the 26.1 branch instead of master, since the workflow reads conf.py from the 26.1 branch.