feat(indexing): add index-file-document tool for file uploads

[adityamparikh]

Summary

Adds a new MCP tool index-file-document that enables users to upload files of any format (PDF, Word, Excel, PowerPoint, etc.) through their AI chat client and have the content indexed into Solr for full-text search.

Closes #69

How it works

When a user uploads a file in an AI chat client like Claude Desktop, the client handles text extraction — not the MCP server. Here's the flow:

1. User uploads a file (e.g., report.pdf) in Claude Desktop
2. Claude Desktop extracts text from the PDF before Claude ever sees it — Claude receives the readable text content, not the raw binary bytes
3. Claude calls the index-file-document tool, passing the extracted text as content and the original filename (report.pdf) as filename
4. The MCP server indexes a SolrInputDocument with id (auto-generated UUID), content (the full text), and filename (for filtering/display)
5. User can now search over the indexed content using existing search tools

This design means no binary parsing library (Tika, Docling, etc.) is needed on the server side — the AI chat client already does the heavy lifting of text extraction before invoking MCP tools. This keeps the server lightweight and avoids ~100MB of transitive dependencies.

Tool signature

index-file-document(collection, content, filename)

Parameter	Description
collection	Solr collection to index into
content	Text content extracted from the file by the chat client
filename	Original filename with extension (e.g. report.pdf) — stored as a searchable field

Changes

• FileDocumentCreator (new) — @Component that creates a SolrInputDocument with id, content, and filename fields. Does not implement SolrDocumentCreator because it requires a filename parameter in addition to content.
• IndexingDocumentCreator — Added FileDocumentCreator dependency and createSchemalessDocumentsFromFile() delegation method
• IndexingService — New indexFileDocument() MCP tool with @PreAuthorize("isAuthenticated()")
• AGENTS.md — Updated architecture docs

Test plan

• FileDocumentCreatorTest — 9 unit tests: valid input, null/empty/blank content, null/empty filename, oversized content, unique IDs, multiline content
• FileIndexingTest — Spring Boot integration test through IndexingDocumentCreator
• IndexingServiceTest — 2 new Testcontainers integration tests verifying index-then-search round-trip (search by content, search by filename)
• IndexingServiceTest.UnitTests — 2 new mocked unit tests for the MCP tool method
• Existing test constructors updated for new FileDocumentCreator parameter
• ./gradlew build passes with all tests green

🤖 Generated with Claude Code