feat(scheduler): use go-cron FullParser for extended cron syntax (#438)

## Summary

Switch from custom parser configuration to `cron.FullParser()` which
enables all cron syntax variants:

- Standard 5-field cron expressions
- 6-field with optional seconds
- **Year field support** for one-time scheduling (addresses #344)
- **Extended syntax**: L (last), W (weekday), # (nth), #L (last
occurrence)
- Hash expressions for consistent random scheduling
- All cron descriptors (@Yearly, @every, etc.)

## Changes

- **core/scheduler.go**: Replace manual parser config with
`cron.FullParser()`
- **go.mod/go.sum**: Update go-cron dependency to v0.8.0
- **docs/QUICK_REFERENCE.md**: Add examples for year field and extended
syntax

## New Schedule Examples

```bash
# One-time scheduling with year field
30 14 25 12 * 2025         # Dec 25, 2025 at 14:30

# Extended syntax
0 12 L * *                 # Last day of every month at noon
0 12 * * FRI#3             # 3rd Friday of every month
0 12 * * FRI#L             # Last Friday of every month
```

## Test plan

- [x] Existing tests pass (`make test`)
- [x] go-cron v0.8.0 includes comprehensive FullParser tests
- [ ] Manual verification of year field scheduling

Author: CybotTM

core/scheduler.go

@@ -73,10 +73,7 @@ func NewSchedulerWithClock(l Logger, cronClock *CronClock) *Scheduler {
 func newSchedulerInternal(l Logger, metricsRecorder MetricsRecorder, minEveryInterval time.Duration, cronClock *CronClock) *Scheduler {
 	cronUtils := NewCronUtils(l)
 
-	parser := cron.MustNewParser(
-		cron.SecondOptional | cron.Minute | cron.Hour |
-			cron.Dom | cron.Month | cron.Dow | cron.Descriptor,
-	)
+	parser := cron.FullParser()
 	if minEveryInterval != 0 {
 		parser = parser.WithMinEveryInterval(minEveryInterval)
 	}

docs/QUICK_REFERENCE.md

@@ -70,6 +70,17 @@ export OFELIA_PPROF_ADDRESS=127.0.0.1:8080
 0 0 */4 * * *              # Every 4 hours
 0 */30 * * * *             # Every 30 minutes
 
+# With year field (one-time scheduling)
+30 14 25 12 * 2025         # Dec 25, 2025 at 14:30 (one-time job)
+0 30 14 25 12 * 2025       # Same with seconds field
+0 0 1 1 * 2025-2027        # Jan 1 at midnight, 2025-2027
+
+# Extended syntax (L, W, #)
+0 12 L * *                 # Last day of every month at noon
+0 12 15W * *               # Nearest weekday to 15th at noon
+0 12 * * FRI#3             # 3rd Friday of every month at noon
+0 12 * * FRI#L             # Last Friday of every month at noon
+
 # Descriptors
 @yearly                    # 0 0 1 1 *
 @annually                  # 0 0 1 1 *

go.mod

@@ -18,7 +18,7 @@ require (
 	github.com/jessevdk/go-flags v1.6.1
 	github.com/manifoldco/promptui v0.9.0
 	github.com/mitchellh/mapstructure v1.5.0
-	github.com/netresearch/go-cron v0.7.1
+	github.com/netresearch/go-cron v0.8.0
 	github.com/opencontainers/image-spec v1.1.1
 	github.com/sirupsen/logrus v1.9.3
 	github.com/stretchr/testify v1.11.1

go.sum

@@ -109,8 +109,8 @@ github.com/moby/term v0.5.2 h1:6qk3FJAFDs6i/q3W/pQ97SX192qKfZgGjCQqfCJkgzQ=
 github.com/moby/term v0.5.2/go.mod h1:d3djjFCrjnB+fl8NJux+EJzu0msscUP+f8it8hPkFLc=
 github.com/morikuni/aec v1.0.0 h1:nP9CBfwrvYnBRgY6qfDQkygYDmYwOilePFkwzv4dU8A=
 github.com/morikuni/aec v1.0.0/go.mod h1:BbKIizmSmc5MMPqRYbxO4ZU0S0+P200+tUnFx7PXmsc=
-github.com/netresearch/go-cron v0.7.1 h1:4uhkNSWTR3mBVlY1JtIcnZEaSLirTwkLksKy+fXgJw4=
-github.com/netresearch/go-cron v0.7.1/go.mod h1:oRPUA7fHC/ul86n+d3SdUD54cEuHIuCLiFJCua5a5/E=
+github.com/netresearch/go-cron v0.8.0 h1:2kgxsBMAFONMWQvhFbFIlc1xO6upNs/jJ7D7OAFzKmw=
+github.com/netresearch/go-cron v0.8.0/go.mod h1:oRPUA7fHC/ul86n+d3SdUD54cEuHIuCLiFJCua5a5/E=
 github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8Oi/yOhh5U=
 github.com/opencontainers/go-digest v1.0.0/go.mod h1:0JzlMkj0TRzQZfJkVvzbP0HBR3IKzErnv2BNG4W4MAM=
 github.com/opencontainers/image-spec v1.1.1 h1:y0fUlFfIZhPF1W537XOLg0/fcx6zcHCJwooC2xJA040=