chore: land the remaining low-severity items from the whole-project review

Phase 11 of PROJECT_REVIEW_PLAN.md: the themed cleanup pass over every
low-severity finding still open (2.2-2.3, 3.4-3.6, 4.3-4.7, 6.4-6.7,
7.1-7.3, 8.2-8.3, 9.1-9.4, and the under-documented decisions in §10/§11).

Behavioral fixes:
- Reassign duplicate job IDs in a hand-edited jobs.json instead of letting
  two jobs share one runtime, schedule entry, and SeedStats bucket.
- Disambiguate run-log file names that collide within the same second.
- Compute AvgDurationMS as DurationSumMS/TimedRunCount instead of an
  incremental integer mean, so it always matches the seeded-from-logs
  average instead of drifting from truncation error.
- Clean absolute paths in ResolveConfiguredPath so two spellings of the
  same jobs file do not trigger a spurious adoption.
- Report InstallDesktopIcon failures through ErrorOccurred instead of
  discarding them silently.
- Move settingsView's blocking AutostartStatus (PowerShell on Windows) off
  the UI thread.
- Give notify-timing.tsv its own extension so CleanupLogs no longer
  manages it as a run log.
- Replace the settingsView Save handler's second copy of validateConfig's
  rules with a bare parse, letting the Service's own error surface.

Cleanups:
- Delete collectActivity, the dead yaml tags on RunRecord, and the
  logArguments/LogArguments alias.
- Fold the two systemTrayRegistered/mainWindowHidden globals into one
  trayState instance Run owns and threads through Settings and the
  single-instance reveal path.
- Fix stale comments/docs: the frozen window-size restore claim, a
  reference to a renamed recordRun, README's "Pause all" and notification
  wording, the PowerShell quoting note for TESTS.md's coverage command,
  and scripts/test.bat's UTF-8 checkmarks under a non-UTF-8 code page.
- Document the single-instance fallback's consequence and the
  unauthenticated instance-channel port in STANDARDS.md; record the
  config-shim retirement plan in ROADMAP.md.

3.5, 7.3, and 9.4 turned out to already be fixed by earlier phases; no
change needed for those three.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -237,8 +237,9 @@ applies to them — and so measure launch latency only.
 | `RunCount` | total runs recorded |
 | `FailCount` | runs that exited non-zero |
 | `LastDurationMS` | wall-clock time of the most recent run (launch latency for `StartOnly`) |
-| `AvgDurationMS` | mean over all runs with a recorded duration |
+| `AvgDurationMS` | mean over all runs with a recorded duration, computed as `DurationSumMS / TimedRunCount` on every update rather than folded incrementally, so it never disagrees with the exact sum/count average `runner.aggregateLogStats` computes when seeding from logs |
 | `MaxDurationMS` | longest recorded run |
+| `DurationSumMS` | running total of every timed run's duration; the source `AvgDurationMS` is divided from |
 
 `runner.RunJob` measures the wall-clock start→finish and sets `DurationMS` on
 the returned `RunRecord`. `runner/logfile.go` writes a `duration` line into the