Revert "Feature: graph tool"

[idosal]

Reverts #169

[Copilot]

Pull Request Overview

This PR reverts a previously implemented "graph tool" feature that provided code analysis and usage example functionality. The revert removes the entire graph-based code search system that was integrated with FalkorDB.

• Removes the graph tool implementation entirely including GraphCreationService and graph utilities
• Eliminates the fetchUsageCodeExamples tool from the DefaultRepoHandler
• Removes FalkorDB dependency and related configuration

Reviewed Changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/api/tools/repoHandlers/graphTools.ts	Complete removal of graph tools module including FalkorDB integration, configuration, and GraphCreationService
src/api/tools/repoHandlers/graphTools.test.ts	Complete removal of comprehensive test suite for graph functionality
src/api/tools/repoHandlers/DefaultRepoHandler.ts	Removal of fetchUsageCodeExamples tool and graph-related imports
src/api/tools/index.test.ts	Updates to test expectations removing fetchUsageCodeExamples tool
package.json	Removal of falkordb dependency
.env.example	Removal of code graph backend configuration variables

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