feat: read MUX_BASE_URL from env-file and persist to config

[jrmann100]

Note

This was authored by @claude, not @jrmann100.

Summary

• Parses MUX_BASE_URL from --env-file during mux login
• If nonstandard (not https://api.mux.com), saves it as baseUrl in the environment's config.json
• getMuxBaseUrl() now checks: env var > config > default, so subsequent commands use the configured base URL without needing the env var set
• whoami displays API endpoint when using a nonstandard base URL

Test plan

• All 699 existing + new tests pass
• mux login --env-file with a .env containing MUX_BASE_URL=https://api.staging.mux.com saves baseUrl to config
• mux login --env-file without MUX_BASE_URL does not add baseUrl to config
• mux whoami uses the stored baseUrl without MUX_BASE_URL env var set
• mux whoami shows API endpoint only when nonstandard

🤖 Generated with Claude Code

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Note

Medium Risk
Changes how the CLI chooses the API endpoint and persists it to config, which can redirect all subsequent API calls for an environment if misconfigured; scope is contained and covered by new tests.

Overview
Adds support for a configurable Mux API endpoint: mux login --env-file now parses MUX_BASE_URL, validates credentials against that URL, and persists a non-default baseUrl into the saved environment config.

Updates base-URL resolution to prefer MUX_BASE_URL env var, then per-environment config, then the default; commands that fetch from the API (whoami, webhook listen, error permission probing) now use the resolved base URL, and whoami prints the active endpoint when non-default. Includes new/updated tests for .env parsing and getMuxBaseUrl precedence.

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[jrmann100]

@cursor review if you would be so kind?

[cursor]

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