chore: Bump version to 1.16.0-rc1

[QuantumGhost]

AI disclosure: This PR was AI-assisted with Codex using GPT-5.4.
I have reviewed the final diff, and I am responsible for the content.

Summary

• Bump the Dify API package version to 1.16.0-rc1.
• Bump the Dify web package version to 1.16.0-rc1.
• Bump the Dify Agent package version to 1.16.0-rc1.
• Update Docker Compose API, web, and Dify Agent image tags to 1.16.0-rc1.
• Sync the local dify-api and dify-agent package versions in uv lockfiles.

Fixes #38599

Validation:

• uv lock --project dify-agent
• uv lock --project api
• uv lock --project dify-agent --check
• uv lock --project api --check
• node -e "JSON.parse(require('fs').readFileSync('web/package.json', 'utf8'))"
• docker compose -f docker/docker-compose.yaml config --quiet --no-env-resolution
• docker compose -f docker/docker-compose-template.yaml config --quiet --no-env-resolution
• docker compose -f docker/docker-compose.yaml config --images --no-env-resolution | rg 'langgenius/dify-(api|web|agent-local-sandbox|agent-backend):'
• docker compose -f docker/docker-compose-template.yaml config --images --no-env-resolution | rg 'langgenius/dify-(api|web|agent-local-sandbox|agent-backend):'
• git diff --check

Screenshots

Before	After
N/A	N/A

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

From Codex