v6.0.20: Narayana Dasha (Rishi Dasha) implementation

Narayana Dasha is Parashara's rashi-based dasha system, complementary to
Vimshottari (nakshatra-based). Algorithm: start from Lagna, each sign's
dasha years = count from the sign to its lord's sign (zodiacal order).

Implementation:
- scripts/narayana_dasha.py: core calculation module
  - calc_narayana_mahadasha(): 12-sign sequence from Lagna
  - calc_narayana_antardasha(): sub-periods within each MD
  - get_current_narayana_dasha(): locate current period by age
- scripts/cmd_narayana_dasha.py: CLI subcommand
- jyotish_engine.py: Step 4.13 in full-reading + narayana-dasha subparser

Verified with Leo Asc chart: total cycle 88 years, current Sagittarius MD
(31-38 yrs, 5H/creativity) complements Vimshottari Saturn MD.

Files: +2 new (narayana_dasha.py, cmd_narayana_dasha.py), +4 modified

references/technique_registry.json

@@ -1,5 +1,5 @@
 {
-  "version": "v6.0.19-sr-degraded-mode-fix",
+  "version": "v6.0.20-narayana-dasha",
   "source_inspiration": [
     {
       "name": "jyotishyamitra",
@@ -818,6 +818,28 @@
       ],
       "audit_label": "Bhrigu Pada Dasha",
       "missing_impact": "Bhrigu 足步推进法缺失，婚姻时机精确预测受限（通用近似版已实现）。"
+    },
+    "narayana_dasha": {
+      "name": "Narayana Dasha (Rishi Dasha / Padakrama Dasha)",
+      "domains": [
+        "dasha",
+        "rashi",
+        "timing",
+        "narayana"
+      ],
+      "status": "covered",
+      "knowledge_refs": [
+        "bphs-ch48-narayana-dasha.md"
+      ],
+      "commands": [
+        "narayana-dasha",
+        "full-reading"
+      ],
+      "output_paths": [
+        "modules.narayana_dasha"
+      ],
+      "audit_label": "Narayana Dasha",
+      "missing_impact": "N/A - implemented in v6.0.20"
     }
   },
   "routes": {
@@ -963,7 +985,8 @@
         "muntha",
         "prashna_integration",
         "bhrigu_pada_dasha",
-        "solar_return"
+        "solar_return",
+        "narayana_dasha"
       ],
       "optional_techniques": [
         "bhava_chalit",