fix: surface actionable error when config file is not writable

[robingenz]

Summary

• When the CLI cannot read or write ~/.capawesome because of OS permissions (e.g. the file was created during a previous sudo run and is now owned by root), it threw a raw EACCES that bubbled up to Sentry with no guidance for the user.
• UserConfigImpl.read / write now catch the failure and re-throw a UserError carrying the resolved path and a suggested remediation (chown or rm). UserError is already filtered out of Sentry reporting in src/index.ts, so these environment issues stop polluting the issue tracker.
• Added getCodeFromUnknownError in src/utils/error.ts to extract code from unknown errors in a type-safe way, and used it for the EACCES check.

Test plan

• npx tsc --noEmit
• npx vitest run src/commands/login.test.ts src/commands/logout.test.ts src/commands/whoami.test.ts
• npm run fmt

[Copilot]

Pull request overview

Improves the CLI’s handling of permission issues with the user config file (.capawesome) by converting low-level filesystem access errors into actionable UserErrors that are excluded from Sentry reporting.

Changes:

• Catch config read/write permission failures in UserConfigImpl and rethrow a guidance-focused UserError.
• Add getCodeFromUnknownError utility to safely extract an error code from unknown errors for branching (e.g., EACCES checks).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
src/utils/user-config.ts	Wraps rc9 read/write failures to surface actionable permission-denied remediation to the user.
src/utils/error.ts	Adds getCodeFromUnknownError helper used to detect access-denied errors safely.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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