claude-profile: bump opus to 4.8, add fable driver

- driver_model_id(): opus -> claude-opus-4-8, opus-1m -> claude-opus-4-8[1m]
- driver_model_id(): add fable -> claude-fable-5
- error message updated: Valid: haiku sonnet opus opus-1m fable
- spec: driver->model table updated (opus 4.8, fable added); frontmatter
  driver enum includes fable; note that opus-1m retained for [1m] convention
- tests: add Test 13 (deep-fable dryrun asserting claude-fable-5);
  add Test 14 (unknown driver exits 1) — 47 assertions total
  Note: deep-fable mode file lands in the next commit

tests/test-claude-profile.sh

@@ -177,6 +177,63 @@ rc=$?
 assert_exit_code "unknown flag exits 1" 1 "$rc"
 assert_contains "unknown flag error message" "Unknown flag" "$out"
 
+# === Test 13: deep-fable dryrun (deep-fable mode file lands in the next commit) ===
+echo
+echo "Test 13: deep-fable mode dryrun"
+out=$(run --dryrun oreillyit-anthropic --mode deep-fable)
+rc=$?
+assert_exit_code "deep-fable dryrun exits 0" 0 "$rc"
+assert_contains "deep-fable uses fable driver" "Driver:          fable" "$out"
+assert_contains "deep-fable shows fable model ID" "Model ID:        claude-fable-5" "$out"
+assert_contains "deep-fable shows model in exec command" "claude --model claude-fable-5" "$out"
+
+# === Test 14: error — unknown driver produces exit 1 ===
+echo
+echo "Test 14: error path — unknown driver"
+# Create a temporary mode file with an unknown driver in the actual modes dir,
+# run the test, then remove it immediately.
+baddriver_file="$REPO_ROOT/data/claude-profile/modes/_test-baddriver.md"
+cat > "$baddriver_file" <<'MEOF'
+---
+name: _test-baddriver
+tag: bad
+driver: notadriver
+async_ok: no
+autoloop: none
+plan_mode_auto: no
+spec_driven: no
+escalates_to: none
+---
+
+# Mode: Bad Driver Test
+## Purpose
+Temporary test fixture — do not use.
+## Driver constraint
+Unused.
+## Subagent policy
+Unused.
+## Reasoning posture
+Unused.
+## Async policy
+Unused.
+## Workflow stance
+Unused.
+## Auto-fire at session start
+none
+## Status line format
+none
+## Escalation triggers
+none
+## Out of scope
+none
+## On context wipe (/clear)
+none
+MEOF
+out=$(run --dryrun oreillyit-anthropic --mode _test-baddriver 2>&1); rc=$?
+rm -f "$baddriver_file"
+assert_exit_code "unknown driver exits 1" 1 "$rc"
+assert_contains "unknown driver error message" "Unknown driver" "$out"
+
 # === Summary ===
 echo
 echo "================================"