Support custom aliases for OpenAI/Claude account labels

Feature request

Currently, accounts added via jcode login --provider openai (and similarly for Claude) are stored with auto-numbered labels (openai-1, openai-2, ...) based on positional order in the accounts array. relabel_accounts() in jcode-base/src/auth/account_store.rs runs on every load_auth_file() and force-renumbers any label back to the canonical <prefix>-<index> scheme.

This means:

• You cannot set a persistent custom alias (e.g. personal, work, codex-alt) for an account — it gets reset to openai-N on next load.
• Reordering/swapping accounts in the underlying JSON file works to change which number an account gets, but there's no way to give it a memorable name.

Suggested behavior

Allow an optional custom alias field on OpenAiAccount / the Claude equivalent that:

• Is preserved across relabel_accounts() calls (i.e. skip renumbering when a custom alias is present, or keep alias separate from the canonical positional label used internally for override matching).
• Is settable via a CLI/TUI flow, e.g. /account rename openai-2 work or jcode account rename <label> <alias>.
• Is displayed in the account picker (/account, /account openai, /account claude) alongside or instead of the numbered label.

Context

Came up when manually merging two OpenAI accounts into ~/.jcode/openai-auth.json and wanting to label them by which ChatGPT account they represent instead of arbitrary order-dependent numbers.

Relevant code:

• crates/jcode-base/src/auth/account_store.rs (relabel_accounts, canonical_account_label)
• crates/jcode-base/src/auth/codex.rs (OpenAiAccount, JcodeOpenAiAuthFile)

Start in crates/jcode-base/src/auth/account_store.rs, reading relabel_accounts and canonical_account_label, then inspect OpenAiAccount and JcodeOpenAiAuthFile in crates/jcode-base/src/auth/codex.rs. Trace the account rename entry points and picker flows mentioned in the issue. Done means a custom alias survives loading, can be set through a rename flow, and appears in the OpenAI and Claude account pickers.