SGE template: Signal SIGINT by default to allow R to catch it gracefully

When a job is approaching it's maximum run-time limit, and `--notify` has been specified, SGE sends a `SIGUSR2` 60 seconds before sending a `SIGKILL` (abrupt; not capturable).

R code cannot handle `SIGUSR2` signals, only `SIGINT`. If SGE would signal `SIGINT` instead, we could capture it internally as an `interrupt` condition, and using `tryCatch(..., interrupt = ...)`, `on.exit()`, and likes to gracefully exit, e.g. close connections, checkpoint intermediate results, etc.

# Idea

Update the default SGE template to signal `SIGINT`. Unlike Slurm, there is no user-facing option to change the type of signal in SGE. But we could use Bash traps to capture the `SIGUSR2` and re-signal it as `SIGINT`. Something like:

```bash
#! /bin/bash
...
## Request SGE to send warning signals (SIGUSR2) before run-time limit termination
#$ -notify
...

# Function to catch SGE run-time signals and re-signal as SIGINT
forward_sigint() {
echo "Caught SGE run-time signal. Re-signal as SIGINT to R..."
kill -2 "${R_PID}" 2>/dev/null || true
wait "${R_PID}"
res=$?
echo " - exit code (from signal handler): ${res}"
exit "${res}"
}

# Trap SGE run-time limit signals
trap forward_sigint SIGUSR2

<%= rscript_call %> -e 'batchtools::doJobCollection("<%= uri %>")' &
R_PID=$!
wait "${R_PID}"
res=$?

# Clear the trap on normal exit
trap - SIGUSR2
```

Start with the default SGE template and trace how `rscript_call`, `uri`, and `batchtools::doJobCollection` launch the job. Review the proposed Bash `SIGUSR2` trap and process-wait flow, then verify that an approaching time limit reaches R as `SIGINT` and permits graceful cleanup before termination.

Written by the indexing model from the issue text.