feat(exec): let a provider name stand in for its active account

[jiunbae]

Why

aas exec codex answered Account not found: codex, for a name the rest of the CLI already understands. switch, status and active all take a provider and resolve it to whatever that provider has active — exec and proxy were the two that insisted on an account name.

$ aas e codex          # before: Account not found: codex
$ aas e codex          # after:  runs e-ed@codex
$ aas codex            # the bare form follows too
$ aas e grok           # No active account for provider 'grok'. Name an account, or run: aas switch <account>
$ aas e nope           # Account not found: nope

Design

AccountStore::resolve_run_target reads a name as an account first, then as a provider standing in for that provider's active account.

• Account names win. An account called codex keeps addressing that account rather than becoming unreachable — covered by an_account_named_after_a_provider_wins_over_the_active_account.
• No active account resolves to nothing, rather than picking one. exec turns that into a message naming which of the two lookups failed.
• Aliases resolve like the provider they name (claude-code → claude), since it goes through normalize_provider.
• The bare aas <provider> form follows for free: rewrite_default_exec_args decides what counts as a run target through the same lookup.

Provenance

Written by hand on one of our hosts against v0.1.11 and never committed — found while auditing uncommitted work across the fleet, preserved at wip/jiun-mini-exec-provider-target, and rebased here (18 commits of drift; one conflict in exec.rs, where today's caller_system_home landed in the same spot — both kept).

Verification

• All four branches exercised against the real CLI, as above.
• Five tests: two in store.rs for the resolution order and the account-name-wins case, two in main.rs for the bare form with and without an active account, plus the existing rewrite tests.
• 197 tests pass; clippy/fmt clean.

🤖 Generated with Claude Code

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