chore: minor follow-ups from the #373/#376/#380/#383 reviews #394

Minor follow-ups from the reviews of #373, #376, #380, #383

1. (fix(frontend): invalidate the RI exchange quote when targets change #376) frontend/src/riexchange.ts:1653-1656: the "+ Add target" handler doesn't call invalidateQuote(). After a quote, adding a row leaves Execute visible, so the form and the quote block disagree. No wrong purchase is possible, since the executed set is still the quoted set. Add invalidateQuote() and a test.
2. (fix(frontend): stop double-scaling the Savings Plans group row savings #380) frontend/src/recommendations.ts:1562: the hourly period factor is 1/720, while the backend's canonical hours-per-month is 730 (internal/api/handler_ri_exchange.go:1498-1512), so hourly views are about 1.4% off backend-derived monthly figures. Share one constant.
3. (fix(frontend): floor the marketplace consent dialog's remaining term #383) The marketplace consent dialog note renders "5.000000000000004% below remaining value". Format it as a rounded percentage.
4. (fix(server): advisory lock released on the request context strands a task type in permanent already_running #373) Issue fix(server): advisory lock released on the request context strands a task type in permanent already_running #105's third ask: surface a persistent already_running from HandleScheduledTask as non-200, so a stuck lock is visible to the scheduler/alarms. Also rename the now-unused ctx param of ReleaseAdvisoryLock to _.