test: add unit tests for pkg/config package

[mason5052]

Description of Change

Problem: The pkg/config package has no unit test coverage. This package handles all environment variable parsing, default values, URL parsing, and installation ID management for the entire application.

Solution: Add 14 unit tests covering NewConfig defaults, environment variable overrides, URL parsing, provider server URL defaults, summarizer settings, search engine defaults, and all ensureInstallationID code paths (UUID generation, file read/write, invalid value handling).

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Security update
• Test update
• Documentation update
• Configuration change

Areas Affected

• Core Services (Frontend UI / Backend API)
• AI Agents (Researcher / Developer / Executor)
• Security Tools Integration
• Memory System (Vector Store / Knowledge Base)
• Monitoring Stack (Grafana / OpenTelemetry)
• Analytics & Reporting
• External Integrations (LLM Providers / Search Engines / Security APIs)
• Documentation
• Infrastructure / DevOps

Testing and Verification

Test Configuration

• PentAGI Version: v1.2.0 (master)
• Go Version: 1.24.1
• Host OS: Windows 11

Test Steps

1. Run go test ./pkg/config/... -v

Test Results

=== RUN   TestNewConfig_Defaults
--- PASS: TestNewConfig_Defaults (0.00s)
=== RUN   TestNewConfig_EnvOverride
--- PASS: TestNewConfig_EnvOverride (0.00s)
=== RUN   TestNewConfig_ProviderDefaults
--- PASS: TestNewConfig_ProviderDefaults (0.00s)
=== RUN   TestNewConfig_StaticURL
--- PASS: TestNewConfig_StaticURL (0.00s)
=== RUN   TestNewConfig_StaticURL_Empty
--- PASS: TestNewConfig_StaticURL_Empty (0.00s)
=== RUN   TestNewConfig_SummarizerDefaults
--- PASS: TestNewConfig_SummarizerDefaults (0.00s)
=== RUN   TestNewConfig_SearchEngineDefaults
--- PASS: TestNewConfig_SearchEngineDefaults (0.00s)
=== RUN   TestEnsureInstallationID_GeneratesNewUUID
--- PASS: TestEnsureInstallationID_GeneratesNewUUID (0.02s)
=== RUN   TestEnsureInstallationID_ReadsExistingFile
--- PASS: TestEnsureInstallationID_ReadsExistingFile (0.01s)
=== RUN   TestEnsureInstallationID_KeepsValidEnvValue
--- PASS: TestEnsureInstallationID_KeepsValidEnvValue (0.00s)
=== RUN   TestEnsureInstallationID_ReplacesInvalidEnvValue
--- PASS: TestEnsureInstallationID_ReplacesInvalidEnvValue (0.00s)
=== RUN   TestEnsureInstallationID_ReplacesInvalidFileContent
--- PASS: TestEnsureInstallationID_ReplacesInvalidFileContent (0.01s)
=== RUN   TestNewConfig_CorsOrigins
--- PASS: TestNewConfig_CorsOrigins (0.00s)
=== RUN   TestNewConfig_OllamaDefaults
--- PASS: TestNewConfig_OllamaDefaults (0.00s)
PASS
ok  	pentagi/pkg/config	3.855s

Checklist

• Code follows project coding standards
• Tests added for changes
• All tests pass
• go fmt and go vet run
• Changes are backward compatible

[Copilot]

Pull request overview

Adds initial unit test coverage for backend/pkg/config, focusing on NewConfig() default/env parsing behavior and ensureInstallationID() persistence/validation behavior.

Changes:

• Add unit tests for NewConfig() defaults and selected env var overrides (URLs, provider defaults, summarizer/search defaults, CORS, Ollama).
• Add unit tests for ensureInstallationID() covering generation, reading existing IDs, and invalid-value replacement paths.

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[Copilot]

These tests call NewConfig(), which reads environment variables (and godotenv.Load() may load a local .env) and also may read/write ./data/installation_id via ensureInstallationID(). Setting vars to "" does not actually unset them. To make the defaults tests hermetic and avoid side effects/flakes across dev/CI environments, consider (a) t.Chdir(t.TempDir()) before calling NewConfig() and/or (b) explicitly os.Unsetenv (with cleanup restore) for the env vars whose defaults you assert, rather than t.Setenv(key, "").