Background

This PR is a large framework-level refactor, so I updated the PR title to follow the repository contribution guideline's Conventional Commits format:

refactor(framework): introduce component-based application architecture

The change moves FlowLLM away from the older core / op / gallery / extensions layout and consolidates the runtime around the documented main path:

CLI / Client -> Service -> Application -> Job -> Step -> Component

Target behavior

The intended direction appears to be a cleaner, configuration-driven application framework:

• flowllm.application.Application becomes the main entry point for wiring services, components, and jobs.
• Reusable infrastructure lives under flowllm/components/ and is built around BaseComponent.
• Atomic executable units live under flowllm/steps/ and can be composed into Jobs.
• Implementations are resolved through the component registry and backend names instead of the previous flow/op package structure.
• Default behavior is centralized in flowllm/config/default.yaml, keeping the default flowllm start path discoverable.
• Public runtime models are moved into focused packages such as flowllm.schema, flowllm.enumeration, flowllm.config, and flowllm.utils.

Impact scope

This is best reviewed as a major architectural reset rather than a narrow refactor.

The PR:

• Adds the new component architecture, including lifecycle management, dependency binding, registry lookup, application/runtime context, services, clients, jobs, embedding support, and agent wrappers.
• Adds built-in Jobs and Steps for version, health check, help, demo, add, and streaming demo behavior.
• Reworks config parsing to support named config discovery, YAML/JSON loading, keyword overrides, deep merge behavior, and environment expansion with ${ENV_VAR} / ${ENV_VAR:-default}.
• Refreshes README content and adds English/Chinese documentation for quick start, framework concepts, contribution guidance, and architecture diagrams.
• Reorganizes tests into tests/unit and tests/integration.
• Removes large deprecated surfaces, including much of the previous flowllm.core, flowllm.extensions, flowllm.gallery, legacy vector store code, older docs, and the old/ tree.

Because of the package removals, this should be treated as a breaking change for users importing old modules directly.

Test plan

The PR adds or updates coverage for:

• BaseComponent lifecycle and dependency injection behavior.
• Component registry registration and lookup.
• Runtime context and application config models.
• Config parser behavior, including dot-notation overrides and environment expansion.
• Service behavior and CLI argument handling.
• Common built-in Steps.
• Integration coverage for agent session persistence and forked sessions.

Before merge, the expected validation should match the contribution guide:

pre-commit run --all-files
pytest

For focused checks:

pytest tests/unit
pytest tests/integration

One CI issue should be fixed or confirmed: .github/workflows/unittest.yml currently installs pip install -e ".[dev,core]", but pyproject.toml defines dev, claude-code, and full extras, not core. If the core extra was intentionally removed, CI should probably use .[dev] or .[full].

Review focus

I recommend reviewers focus on these boundaries:

• Whether the new public imports from flowllm.__init__, flowllm.application, flowllm.components, flowllm.schema, and flowllm.steps are the intended stable API.
• Whether removing flowllm.core, flowllm.extensions, and flowllm.gallery is acceptable for this release.
• Whether every default backend in flowllm/config/default.yaml is registered through @R.register(...) and imported by the relevant __init__.py.
• Whether the package entry point flowllm = flowllm.application:main covers the intended quick-start path.
• Whether tests that require LLMs, embeddings, or external services clearly document the required environment, as requested by the contribution guide.