docs: Update outdated documentation pages

[Copilot]

Description

Updates several stale pages on the ONNX Runtime documentation site (sourced from the gh-pages branch), addressing missing content, deprecated APIs, and outdated version information.

Changes by page:

• docs/install/index.md — Adds WebGPU EP install instructions: how to use onnxruntime-web/webgpu import and the ort.webgpu.min.js script tag for browser usage.

• docs/get-started/community-projects.md — Separates Rust from the Julia/Ruby community section; documents the ort crate as the Rust API for ONNX Runtime with a Cargo.toml snippet.

• docs/get-started/training-pytorch.md — Removes the deprecated torch-ort / python -m torch_ort.configure flow; replaces with pip install onnxruntime-training and the correct onnxruntime.training.ortmodule.ORTModule import path.

• docs/performance/model-optimizations/ort-format-models.md — Extends the backwards compatibility table to include 1.15+ (no breaking changes from 1.14).

• docs/reference/operators/index.md — Fills in the previously empty operators index with descriptions of full vs. reduced builds, contrib ops, mobile ops, and links to custom operator guides.

• docs/tutorials/accelerate-pytorch/pytorch.md — Fixes argument order in torch.onnx.export example: (model, PATH, example) → (model, example, "model.onnx").

• docs/get-started/with-python.md — Updates CUDA 11.8 header to CUDA 11.x; removes stale nightly feed entries from the Builds table.

• docs/get-started/with-windows.md — Removes the outdated API contract version table (Windows OS 1809/1903/1909, ORT 1.2–1.4).

Motivation and Context

Several documentation pages listed in the issue were missing information (WebGPU install, Rust API), referencing deprecated packages (torch-ort), or showing obsolete version tables. These updates bring the affected pages in line with current ORT capabilities and recommended practices.

[justinchuby]

@copilot I think you need to rebase on the gh-pages branch

[Copilot]

@copilot I think you need to rebase on the gh-pages branch

Done — rebased onto gh-pages in commit 46725837. The branch now has a single commit on top of 5afdf5efc (latest gh-pages).

[justinchuby]

@MaanavD I wonder if we should just remove this page?

[justinchuby]

@copilot is it possible to update the deployment script to show an last updated tag under the doc page titles? How hard would this be?

[Copilot]

@copilot is it possible to update the deployment script to show an last updated tag under the doc page titles? How hard would this be?

It's definitely doable, but it would require a few coordinated changes and is probably a medium-effort task:

1. Add the jekyll-last-modified-at gem to Gemfile — this plugin reads git log to automatically populate page.last_modified_at for each file without needing manual front matter on every page.

2. Register it in _config.yml under plugins:.

3. Override the just-the-docs layout by creating _layouts/default.html (copying it from the theme) and inserting something like:

   {% if page.last_modified_at %}
   <p class="text-small text-grey-dk-100">Last updated: {{ page.last_modified_at | date: "%B %-d, %Y" }}</p>
   {% endif %}

   right below the page <h1> title.

The main complication is that the layout override needs to stay in sync with upstream just-the-docs theme updates. If you'd like I can implement this in a follow-up PR.