fix(agent): load environment variables when no config file is provided

[s0up4200]

Summary

• The agent command was using config.New() when no --config flag was provided, which skips environment variable loading entirely. Env vars like NETRONOME__AGENT_HOST, NETRONOME__AGENT_PORT, and NETRONOME__AGENT_API_KEY were silently ignored.
• Now uses config.Load() which searches for config files in default paths and always applies environment variable overrides, matching the behavior of the serve command.

Test plan

• Start agent with NETRONOME__AGENT_HOST and NETRONOME__AGENT_PORT env vars set (no --config flag) and verify it binds to the correct address
• Start agent with NETRONOME__AGENT_API_KEY set and verify authentication is enabled
• Start agent with both env vars and CLI flags, verify CLI flags take precedence
• Start agent with --config flag and verify config file + env vars still work as before

Closes #102

Summary by CodeRabbit

• Bug Fixes
  • Improved configuration loading behavior with better default fallback handling.
  • Command-line flags now reliably override configuration file and environment settings for logging level, host, port, interface, API key, and disk inclusion/exclusion options.

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[s0up4200]

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📝 Walkthrough

Walkthrough

Modified config loading in the agent's main function to unconditionally load configuration files, gracefully fall back to defaults on failure, and apply command-line flag overrides with proper precedence after loading. Logger initialization was moved post-config to ensure correct configuration propagation.

Changes

Cohort / File(s)	Summary
Config Loading Refactor cmd/netronome/main.go	Changed from conditional to unconditional config loading; added graceful fallback to defaults on load failure; implemented post-load CLI flag overrides for host, port, interface, api-key, diskIncludes, diskExcludes, and log-level to establish proper config precedence

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰✨ With files loaded true and flags applied with care,
Environment whispers finally heard in the air,
No more defaults when the config should reign,
Precedence flows just right, no more pain! 🎉

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: replacing conditional config loading with unconditional config.Load() to respect environment variables when no config file is provided.
Linked Issues check	✅ Passed	The PR directly addresses issue #102 by ensuring environment variables (NETRONOME__AGENT_HOST, NETRONOME__AGENT_PORT, NETRONOME__AGENT_API_KEY) are loaded and applied when no config file is provided.
Out of Scope Changes check	✅ Passed	All changes are scoped to resolving environment variable loading; no unrelated modifications to other functionality or code areas are present.

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✨ Finishing touches

• 📝 Generate docstrings

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