Per-schedule `timeout_seconds` override

agent.toml has a single timeout_seconds at the [agent] level. But many agents have multiple schedules with very different durations — morning might run a quick health check (10s) and nightly might run a full backup (30 min). Forcing both into the same timeout means either the quick one waits too long to fail or the slow one gets killed unfairly.

Proposal

Allow timeout_seconds to be set per [[schedules]] entry, overriding the agent-level default:

[agent]
timeout_seconds = 60          # default for all schedules

[[schedules]]
id = "morning"
type = "cron"
weekday = "mon-fri"
at = "10:15"
# inherits 60s

[[schedules]]
id = "nightly"
type = "cron"
weekday = "mon-sun"
at = "02:00"
timeout_seconds = 1800        # override: 30 min for the heavy backup

Acceptance criteria

• Schedule-level timeout_seconds parses and overrides the agent-level value at runtime.
• When absent, behavior is identical to today.
• dotagent doctor reports both values in inspect.
• agent-spec.md updated.

Where to start

• crates/dotagent-core/src/manifest.rs — Schedule struct.
• crates/dotagent-runner/src/lib.rs::run — timeout resolution.

Non-goals

• Dynamic timeouts (e.g. "10× the rolling average duration"). Static config only.