docs: fix broken links across the documentation site

[vdusek]

Checked all documentation links with lychee (the same checker used in apify-docs, run over the built site) and fixed the broken ones. Doc-link 404s drop from 379 to 10.

• Frozen versioned API reference: source links were hardcoded to blob/master/…, which started 404ing after the clients/resource_clients/→_resource_clients/ and client.py→_apify_client.py refactor. Pinned them to the immutable version tag (e.g. blob/v2.5.1/…), mirroring how apify-sdk-python pins them to a commit SHA.
• Model docstrings: absolutized relative ](/platform/…) links and fixed the malformed Docker build-cache anchor. Added absolutize_doc_links() to scripts/postprocess_generated_models.py so regeneration keeps them absolute.
• Changelog: corrected release-tag URLs (releases/tags/ → releases/tag/, and v1.3.0 → 1.3.0 since that tag has no v prefix).
• Applied the matching docstring fixes to the committed version snapshots (0.6/1.12/2.5/3.0) so the published pages are correct now.

The remaining 10 are theme/plugin artifacts (changelog "Edit this page" links pointing at generated files, an llms-txt blog.md link, a frozen 1.12 cross-reference) plus a local-only reference/next Docker link that regenerates correctly in CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.51%. Comparing base (3e21ff0) to head (9c9edef).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #865   +/-   ##
=======================================
  Coverage   94.51%   94.51%           
=======================================
  Files          48       48           
  Lines        5069     5069           
=======================================
  Hits         4791     4791           
  Misses        278      278           

Flag	Coverage Δ
integration	92.99% <ø> (+0.19%)	⬆️
unit	83.27% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[vdusek]

relates apify/docusaurus-plugin-typedoc-api#83