Enable Rig's built-in tracing spans (model, token usage, cache hits,
latency) via tracing-subscriber, filterable through RUST_LOG and
defaulting to info level. Logs write to stderr so stdout stays
reserved for program output. Standardizes the remaining ad-hoc
println! diagnostics (server startup, per-iteration revision progress,
non-convergence) into structured tracing events at appropriate levels.
Gemma now seeds deliberately hostile text, Shieldstral scores it, and
Gemma revises its own output based on the score until it drops below a
safety threshold (or a max-iteration cap is hit, returning the best
attempt seen). Extracted into a new revise module: score() now borrows
instead of consuming its args so it can run repeatedly, and the
gemma-call/extract-text logic is shared between seed generation and
every revision instead of being duplicated.
Also adds FINDINGS.md logging what actually turned out to be real
obstacles vs. overblown vs. irrelevant while building this out.
