chore(release): prepare 1.0.0

[leoafarias]

Summary

• Bump all publishable Ack packages to 1.0.0 and update internal dependency constraints to ^1.0.0
• Mark docs metadata and llms.txt as stable 1.0.0
• Add concise 1.0.0 changelog entries and CONTRIBUTING.md
• Clean up remaining contributor-facing stale @AckModel wording

Verification

• dart pub get
• npx @docs.page/cli check
• dart test test/documentation (from packages/ack): 124 passed
• dart analyze . --fatal-infos in packages/ack, ack_annotations, ack_generator, ack_json_schema_builder, example
• flutter analyze . --fatal-infos in packages/ack_firebase_ai
• dart test in packages/ack: 922 passed
• dart test in packages/ack_generator: 130 passed
• dart test in packages/ack_json_schema_builder: 49 passed
• dart test in example: 105 passed
• flutter test in packages/ack_firebase_ai: 98 passed, 4 live tests skipped without credentials
• dart pub publish --dry-run for ack, ack_annotations, ack_generator, ack_json_schema_builder: 0 warnings
• flutter pub publish --dry-run for ack_firebase_ai: 0 warnings

Publish note

After this PR merges, publish by creating the GitHub Release/tag v1.0.0 per PUBLISHING.md. I did not create the tag or publish packages from this branch.

[docs-page]

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docs.page/btwld/ack~120

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