Support bundles previously captured only the active coder-agent.log, losing
history across agent restarts. Add an optional `after` filter to the agent's
/debug/logs endpoint: without it the endpoint is unchanged (active log only,
10 MiB cap); with it the response includes the active log plus rotated
coder-agent-*.log files modified after the cutoff, newest first. Support
bundles request the last 24h.
Closes#25395
