analyze_observations moved observations.jsonl into observations.archive/
unconditionally, even when the Claude analysis failed (timeout, non-zero
exit, rate limit). Because the analyzer only reads the live file, a failed
batch was archived and never re-analyzed, silently dropping the instincts
it would have produced.
Return early on a non-zero analysis exit so the archive mv runs only on
success, retaining observations for the next cycle to retry. Resolve the
script's own directory from ${BASH_SOURCE[0]} (SCRIPT_DIR) so sibling
scripts (session-guardian.sh) and relative helpers resolve correctly under
both execution and sourcing, and add a source-guard so observer-loop.sh can
be sourced without starting the loop. Add a regression test covering both
the failure (retain) and success (archive) paths.
Fixes#2370
