feat(phased-execution): push each phase commit after it is made

The harness now pushes the phase commit right after committing it
(PHASE_PUSH=1 default, new push_phase in lib.sh): upstream when set,
else 'git push -u <first remote> <branch>'; no remote = skip with a
notice. A push failure keeps the commit local, prints the same loud
ERROR contract as a commit failure, and stops the run — the next
phase's push sweeps the unpushed commit in. PHASE_PUSH=0 opts out with
a loud notice. SKILL.md (Commits + config table + exit codes) and the
executor prompts document the new behavior.

phased-execution/scripts/run-phase.sh

@@ -11,7 +11,7 @@
 #   run-phase.sh 03_api.md    # a legacy single-file phase
 #
 # Env: see SKILL.md (MAX_FIX_ATTEMPTS, PHASE_MODEL, PHASE_THINKING,
-#      PHASE_COMMIT, PI_TRUST, FRESH_FIX).
+#      PHASE_COMMIT, PHASE_PUSH, PI_TRUST, FRESH_FIX).
 set -uo pipefail
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 source "$SCRIPT_DIR/lib.sh"
@@ -45,7 +45,7 @@ while unit="$(phase_next_unit "$phase")"; do
 done
 if (( failed )); then
   # execute_unit printed the failure detail (task failure: errors, logs,
-  # resume command — or phase-commit failure: the hand-fix command).
+  # resume command — or phase commit/push failure: the hand-fix command).
   echo "✗ ERROR: phase $phase did not complete — see the error output above" >&2
   exit 1
 fi