Define run tracking modes (`strict-run` and `follow-descendants`)

[melonattacker]

Is your feature request related to a problem? Please describe.

logira run currently tracks the executed command and its descendants, but the behavior around long-lived child processes is unclear.

Examples include:

• agents spawning background processes
• daemonized children
• processes that continue running after the parent exits

It is not obvious whether logira should:

• stop tracking when the parent exits
• continue tracking descendants
• or detect and report escaped processes

Clear semantics would help users understand how runs are bounded.

Describe the solution you'd like

Introduce explicit run tracking modes.

strict-run

Default mode for auditing a single command.

Behavior:

• track the parent command and its descendants
• close the run when the parent exits
• allow a short grace period
• report if descendants remain running

Example:

logira run --mode strict-run -- claude

follow-descendants

Continue tracking descendant processes after the parent exits.

Behavior:

• keep tracking children until they exit
• or until a timeout / linger period
• surface persistent background processes

Example:

logira run --mode follow-descendants --linger 60s -- claude

Describe alternatives you've considered

One option is to keep the current behavior and document it more clearly.

However, different use cases require different run boundaries:

• auditing a single command
• tracking agents that spawn background tasks

Explicit modes provide flexibility without complicating the basic workflow.

Additional context

This also prepares the groundwork for service-style monitoring (logira watch) where process lifetimes may not map cleanly to a single command invocation.