feat(nodes): add managed file inputs

[Gohankaiju]

Summary

Closes #9300

This PR adds a first pass of managed file inputs for custom nodes.

It introduces a lightweight FileField flow so node authors can accept document/data files through the InvokeAI UI, instead of requiring users to provide server-local paths or embedding file contents in workflow data. This is especially important for hosted deployments, but is also useful for local/self-hosted users because files can be attached directly from the node input UI.

What is included:

• FileField invocation field support
• Managed file upload/get/delete API
• Node input UI for uploading and clearing a file reference
• Server-managed file storage using stable file_id references
• Invocation-side access via context.files
• Extension/MIME allowlists and configurable upload size limit
• Upload body size limiting for the managed file upload endpoint
• Backend tests
• Regenerated OpenAPI schema and frontend API types

This first pass is intentionally scoped to node inputs. It does not add gallery/boards integration, previews, thumbnails, search, starring, or bulk file management.

Clearing a node input currently removes the node's reference only. Automatic server-side deletion is left out for now because the same file_id may still be referenced by saved workflows, copied nodes, or queued executions.

Related Issues / Discussions

Refs #9300

QA Instructions

Automated checks run locally:

uv run ruff check invokeai/app/api_app.py invokeai/app/api/dependencies.py invokeai/app/api/routers/files.py invokeai/app/services/config/config_default.py invokeai/app/services/files tests/app/services/files/test_files_disk.py
uv run --extra test pytest tests/app/services/files/test_files_disk.py
uv run python -m compileall -q invokeai/app/api_app.py invokeai/app/api/dependencies.py invokeai/app/api/routers/files.py invokeai/app/services/files invokeai/app/services/shared/invocation_context.py invokeai/app/services/invocation_services.py invokeai/app/invocations/fields.py invokeai/invocation_api/__init__.py
corepack pnpm@10.12.4 -C invokeai/frontend/web exec eslint --max-warnings=0 src/features/nodes/components/flow/nodes/Invocation/fields/inputs/FileFieldInputComponent.tsx src/services/api/endpoints/files.ts
corepack pnpm@10.12.4 -C invokeai/frontend/web lint:tsc
uv run python scripts/generate_openapi_schema.py | corepack pnpm@10.12.4 -C invokeai/frontend/web typegen
git diff --check

Startup smoke test:

uv run invokeai-web --root /tmp/invokeai-managed-file-review-startup

Confirmed startup reached Invoke running on http://127.0.0.1:9090.

Still validating before marking ready for review:

• End-to-end custom node workflow using FileField
• Browser upload of a PDF into a node input
• Invocation-side file access through context.files

Merge Plan

Draft PR for design and implementation feedback.

No database schema migration is included. No gallery/boards file lifecycle is introduced in this first pass.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration (N/A: adds handling for a new field value type; does not migrate existing persisted state)
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)