Make MultiAgentV2 wait minimum configurable (#20052)

## Why

MultiAgentV2 `wait_agent` currently clamps short waits to a fixed 10
second minimum. That default is still useful for preventing tight
polling loops, but it is too rigid for environments that need faster
mailbox wake-up checks or a larger minimum to discourage frequent
polling.

This PR makes the minimum wait timeout configurable from the existing
MultiAgentV2 feature config section, so operators can tune the behavior
without changing the legacy multi-agent tool surface.

## What Changed

- Added `features.multi_agent_v2.min_wait_timeout_ms`.
- Defaulted the new setting to the existing 10 second floor.
- Validated the configured value as `1..=3600000`, matching the existing
one hour maximum wait bound.
- Applied the configured minimum to MultiAgentV2 `wait_agent` runtime
clamping.
- Plumbed the configured minimum into the `wait_agent` tool schema,
including the effective default when the minimum is above the normal 30
second default.
- Regenerated `core/config.schema.json`.

## Verification

- `cargo test -p codex-features`
- `cargo test -p codex-tools`
- `cargo test -p codex-core --lib multi_agent_v2`
- `just fix -p codex-core`

codex-rs/core/config.schema.json

@@ -1336,6 +1336,12 @@
           "minimum": 1.0,
           "type": "integer"
         },
+        "min_wait_timeout_ms": {
+          "format": "int64",
+          "maximum": 3600000.0,
+          "minimum": 1.0,
+          "type": "integer"
+        },
         "root_agent_usage_hint_text": {
           "type": "string"
         },