fix(config): guard the emission-date probes against absent formats

The generic emissionDate rule ran unconditionally: on a document whose
date is not numeric (e.g. "le 19 janvier 2026"), date(firstMatch(...))
errored on the empty match and routed a correctly classified document to
pending/. Each format probe now checks for its own format first, and a
frDate fallback handles French natural-language dates.

archivist/config.jsonc

@@ -43,6 +43,10 @@
   //   the first page, pages[0:3] searches pages 1 to 3 (expr slice
   //   syntax, end exclusive), any list of strings works; omitted = the
   //   whole document.
+  //   frDate(text) parses a French natural-language date ("le 19 janvier
+  //   2026"; the day is optional and "1er" / abbreviated months are
+  //   accepted) into a native date, for documents whose date is not
+  //   written in a Go layout format.
   //   period(value, unit, shift, layout?) renders a period instead of a
   //   raw date: unit = `month`|`quarter`|`half`|`year`, shift = -1/0/+1
   //   for the previous / containing / next period (rent receipt: 0,
@@ -59,13 +63,25 @@
     // --- Generic extraction, runs for every document -------------------------
     // Emission date, e.g. "Paris, le 15/01/2026" -> "15/01/2026" (parsed
     // into a native date; named emissionDate to avoid clashing with the
-    // expr date() builtin)
+    // expr date() builtin).
+    // Every format probe is guarded by its own "when": an unguarded
+    // date(firstMatch(...)) on a document that does not carry the format
+    // is a rule error, and a single rule error routes a perfectly
+    // classifiable document to pending/ (US-15).
     {
-      "when": "true",
+      "when": "firstMatch(`[0-9]{2}/[0-9]{2}/[0-9]{4}`, pages[0]) != ``",
       "set": [
         { "field": "emissionDate", "eval": "date(firstMatch(`[0-9]{2}/[0-9]{2}/[0-9]{4}`, pages[0]), `02/01/2006`)" }
       ]
     },
+    // Fallback: French natural-language date, e.g. "le 19 janvier 2026",
+    // when the page carries no numeric date.
+    {
+      "when": "firstMatch(`[0-9]{2}/[0-9]{2}/[0-9]{4}`, pages[0]) == `` && firstMatch(`(?:le )?[0-9]{1,2} [A-Za-zÀ-ÿ]{3,} [0-9]{4}`, pages[0]) != ``",
+      "set": [
+        { "field": "emissionDate", "eval": "frDate(firstMatch(`(?:le )?[0-9]{1,2} [A-Za-zÀ-ÿ]{3,} [0-9]{4}`, pages[0]))" }
+      ]
+    },
 
     // --- Bank statements (relevés de compte) ----------------------------------
     {