Stop run_psa dropping the first parameter column

[jurjoroa]

Goal

run_psa calls make_psa_obj(parameters = psa_samp[, -1]) unconditionally, so a hand-built psa_samp silently loses its first real parameter from $parameters and $parnames even though that parameter still drives FUN and the computed outcomes. Separately, the FUN-validity guard in the same file is dead code — is.na(sum(is.na(x))) is always FALSE, so the intended friendly error never fires.

Scope

• At R/run_psa.R:121, drop the leading column only when it is the nsamp index column that gen_psa_samp() prepends
• At R/run_psa.R:47, replace the inert guard with a tryCatch success flag so FUN is not well defined is actually raised
• Add regression tests in tests/testthat/test_run_psa.R for a hand-built psa_samp and for a misdefined FUN
• Re-verify the audit repro on-branch before applying the proposed diff — this fix was reasoned from root cause, not re-run to green

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Version: #172