chore: prepare v0.6.13 release

[leehack]

Summary

• Bump package version to 0.6.13.
• Promote accumulated Unreleased notes into the 0.6.13 changelog section.
• Update current README/docs install snippets and recent release highlights.
• Refresh the chat app lockfile path-dependency version.

Release scope

• Model source download/cache manager APIs and hardening.
• LlamaEngine.loadModelSource(...) native/web routing.
• KV-cache state persistence APIs and WebGPU bridge forwarding for bridge assets v0.1.15+.
• No public API breaking changes; existing loadModel(...) callers remain unchanged.

Test Plan

• dart pub get
• (cd example/chat_app && flutter pub get)
• dart format --output=none --set-exit-if-changed .
• dart analyze
• dart test
• ./tool/docs/build_site.sh
• ./tool/docs/validate_links.sh
• dart pub publish --dry-run
• Independent release-prep review: passed, no blockers.

Notes

• Per release workflow, the actual publish/docs-version automation should run from tag v0.6.13 after this PR merges.

[Copilot]

Pull request overview

Prepares the v0.6.13 release by updating the package version and promoting the accumulated release notes into the 0.6.13 sections, while keeping README and docs install snippets aligned with the new published version.

Changes:

• Bumped llamadart package version to 0.6.13 and refreshed the example app path-dependency lockfile entry.
• Promoted Unreleased notes into ## 0.6.13 in both CHANGELOG.md and the docs “Recent Releases” page.
• Updated README and docs installation snippets to reference ^0.6.13.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
website/docs/getting-started/installation.md	Updates install snippet to llamadart: ^0.6.13.
website/docs/changelog/recent-releases.md	Promotes “Unreleased” section to 0.6.13 release highlights.
README.md	Updates dependency snippet to ^0.6.13.
pubspec.yaml	Bumps package version to 0.6.13.
example/chat_app/pubspec.lock	Updates locked path dependency version to 0.6.13.
CHANGELOG.md	Promotes top section from “Unreleased” to 0.6.13 and refines compatibility note wording.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.32%. Comparing base (40acad3) to head (b9256cb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #147   +/-   ##
=======================================
  Coverage   78.32%   78.32%           
=======================================
  Files          75       75           
  Lines        9764     9764           
=======================================
  Hits         7648     7648           
  Misses       2116     2116           

Flag	Coverage Δ
unittests	78.32% <ø> (ø)

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