Give monitorctl and monitord a real front door

[evandhoffman]

Summary

• Both CLIs are now ParsableCommands (swift-argument-parser), so --help is rendered from the @Option/@Flag declarations and an unrecognised flag is refused by the same table. A flag added here appears in --help because there is no second place to add it to. Sources/monitord/Monitord.swift, Sources/monitorctl/Monitorctl.swift.
• --help / -h / help print usage to stdout and exit 0. --version prints the version and the commit it was built from. An unknown flag, a missing value or an unparseable value is named on stderr and exits 64, and nothing starts. A value that parses but cannot work — a non-positive --interval, a --count below one — is rejected in validate().
• Choices come from the type: LogRetention.allValueStrings and the source registry's allIDs, rather than a list written out in prose that was already one literal away from lying.
• SourceRegistry.allIDs becomes a stored property (Sources/MonitorSources/SourceRegistry.swift:27). It called makeAll() on every access, and makeAll() builds real readers — SMCSource opens an IOKit connection. Cheap while the app asked once at launch, and not cheap at all once the list went into a --help string ArgumentParser rebuilds on every parse: the new suite took four minutes before this and takes under a second after it.
• Tradeoff: this adds the package's first third-party dependency, Apple's swift-argument-parser, used only by the two CLI targets — nothing in the app, the UI or the sources links it. Package.resolved is now committed rather than ignored, because a version range resolves to whatever is newest on the day and a release built from a different revision than the one tested is not the release that was tested. AGENTS.md and docs/ui.md drop the no-dependencies rule.

Closes #48

Test plan

• swift test — 257 tests in 32 suites pass. CommandLineTests is new and covers both binaries' front doors, which no other suite touches: the daemons themselves were never broken.

• swift build -c release

• swiftformat Sources Tests Plugins --lint --cache ignore — clean

• The issue's table re-run against the release binaries. All five argv rows now print and exit instead of booting a daemon, and none of them writes a CSV:

  argv	exit	output	CSV
  --help	0	usage	no
  -h	0	usage	no
  help	0	usage	no
  --version	0	1.6.0 (v1.6.0-…)	no
  --nonsense	64	error + usage	no

• CI green, including two new steps: --help/--version against the real release binaries, and an assertion that monitord --help leaves its --dir empty — a daemon booting instead of printing is only visible from outside the process.

Out of scope

The per-fan sensor.fan.N.mode column asked for in the second comment on #48 is a metric change rather than a parsing one, and is not in this PR.