fix: resolve clippy unused_assignments warnings in error.rs

[jdx]

Summary

• Add #![allow(unused_assignments)] to suppress false positives from thiserror/miette macro-generated code
• Improve error messages to use previously unused fields for better debugging context

Changes

Error variants now include more context in their messages:

• ConfigFileNotFound, ConfigReadFailed, ConfigWriteFailed - now show path
• ConfigValidationFailed - now shows list of issues
• ProviderConfigResolutionFailed - now shows details
• AgeIdentityNotFound, AgeIdentityReadFailed - now show path
• AgeIdentityParseFailed, AgeEncryptionFailed, AgeDecryptionFailed - now show details

Test plan

• cargo clippy passes with no warnings

🤖 Generated with Claude Code

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Note

Improves diagnostics and eliminates clippy noise in src/error.rs.

• Adds crate-level #![allow(unused_assignments)] to avoid false positives from thiserror/miette macro-generated code
• Enhances error messages to surface previously unused fields:
  • Config errors (ConfigFileNotFound, ConfigReadFailed, ConfigWriteFailed) now include path; ConfigValidationFailed prints issues
  • Provider errors (ProviderConfigResolutionFailed) now include details
  • Age encryption errors (AgeIdentityNotFound, AgeIdentityReadFailed) now include path; (AgeIdentityParseFailed, AgeEncryptionFailed, AgeDecryptionFailed) include details
• Minor copy tweaks to help text for clarity

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[Copilot]

Pull request overview

This PR resolves clippy unused_assignments warnings in error.rs by adding a module-level allow directive and improving error message formatting to include previously unused fields.

Changes:

• Added #![allow(unused_assignments)] to suppress false positives from thiserror/miette macro-generated code
• Enhanced error messages to include contextual information from struct fields (paths, details, issues)
• Updated one help message to reference "above" instead of "below" to match the new error format

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[Copilot]

The help message refers to 'errors above' but the actual validation issues appear inline within the error message itself (joined with newlines), not above it in the output. Consider changing to 'Review the validation issues and update your fnox.toml file' for clarity.

Suggested change

	help("Review the errors above and update your fnox.toml file")
	help("Review the validation issues and update your fnox.toml file")