Prepare llamadart 0.6.15 release

[leehack]

Summary

• bump llamadart to 0.6.15 for the release prep
• promote the accumulated changelog and website recent-release notes from Unreleased to 0.6.15
• update current install snippets and refresh the chat app lockfile for the local package version

Release notes

• fixes GLM-OCR and other multimodal chat-template workaround serialization for media content, system prompts before leading media parts, and invalid tool-call serialization failures
• adds the local E2E discovery/orchestration entry point for heavyweight Dart, Flutter, and Web smoke scenarios
• hardens the llama.cpp chat/template E2E runner for current upstream target names and build requirements

Validation

• dart format --output=none --set-exit-if-changed .
• git diff --check
• dart analyze
• dart test
• ./tool/docs/build_site.sh
• ./tool/docs/validate_links.sh
• dart pub publish --dry-run (0 warnings)

[Copilot]

Pull request overview

Prepares the llamadart 0.6.15 release by bumping the package version and promoting accumulated “Unreleased” notes into a 0.6.15 section across the changelog and docs, keeping install snippets and the example app lockfile aligned with the new version.

Changes:

• Bumped package version to 0.6.15 and updated install snippets to reference ^0.6.15.
• Promoted “Unreleased” release notes to a 0.6.15 section in CHANGELOG.md and the docs “Recent Releases” page (including a compatibility note).
• Updated the example chat app pubspec.lock to reflect the local package version 0.6.15.

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 dependency snippet to ^0.6.15.
website/docs/changelog/recent-releases.md	Renames the top section to 0.6.15 and adds a compatibility note.
README.md	Updates dependency snippet to ^0.6.15.
pubspec.yaml	Bumps package version to 0.6.15.
example/chat_app/pubspec.lock	Updates the path dependency’s resolved version to 0.6.15.
CHANGELOG.md	Promotes “Unreleased” notes into a 0.6.15 section and adds a compatibility note.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.67%. Comparing base (8625cbf) to head (0a123cc).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #159   +/-   ##
=======================================
  Coverage   78.67%   78.67%           
=======================================
  Files          76       76           
  Lines        9910     9910           
=======================================
  Hits         7797     7797           
  Misses       2113     2113           

Flag	Coverage Δ
unittests	78.67% <ø> (ø)

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