Give the interpreter real Celtic Cross meanings and --format/--lang support

- guidance.c now prints last, after the full spread; both it and main.c's
  new Celtic Cross readout pull real Waite card meanings via tarot_data.c
  instead of just naming cards.
- interpreter-cli gains --format text|html|json and --lang en|de, matching
  deck-engine - required linking engine/src/tarot_data.c and i18n.c into
  the interpreter binary (a narrow, documented exception to its earlier
  "no engine .c files" policy) and writing German translations for
  narrative.c's/guidance.c's own text.

interpreter/src/reading_io.h

@@ -10,18 +10,21 @@
 
 /* Parses deck-engine's `--format json` output (text, null-terminated at
  * text[length]) and fills *out with just enough of a DailyReading for
- * interpret_daily_reading() to work on and for reporting sign/house
- * context around each significant event: out->transits.aspects[]/
- * aspect_count (used for scoring - see significance.c), and
- * out->natal.bodies[]/out->transits.bodies[] (sign + house per body,
- * used only for display). out->natal.ascendant_longitude/houses[] and
- * out->spread are left zeroed - nothing reads them yet.
+ * interpret_daily_reading() to work on, for reporting sign/house context
+ * around each significant event, and for guidance_print()'s tarot
+ * framing: out->transits.aspects[]/aspect_count (used for scoring - see
+ * significance.c), out->natal.bodies[]/out->transits.bodies[] (sign +
+ * house per body, used only for display), and out->spread.positions[]
+ * (card + reversed per Celtic Cross position, used only by
+ * guidance.c). out->natal.ascendant_longitude/houses[] are left zeroed -
+ * nothing reads them yet.
  *
  * Returns false on malformed JSON, or if "transits"."aspects" isn't
  * present as an array (an empty array is fine - that's a real "no
- * aspects today" reading, not an error). A missing/unrecognized entry
- * in "natal"."bodies"/"transits"."bodies" is not an error - see
- * parse_bodies() in reading_io.c. */
+ * aspects today" reading, not an error). A missing/unrecognized entry in
+ * "natal"."bodies"/"transits"."bodies"/"spread"."positions", or a
+ * missing "spread" key entirely, is not an error - see parse_bodies()/
+ * parse_spread() in reading_io.c. */
 bool reading_load_json(const char *text, size_t length, DailyReading *out);
 
 #endif