docs(papra-write-policy): test count 13 → 15 (REQ-INB-31)

`docs/papra-write-policy.md:192` and :202 both said "13 cases"
but `pipelines/_tests/test_papra_decide_offline.py` defines 15
test functions. The v1.1 EXECUTE stage added 2 tests
(test_papra_dry_run_override_wins and
test_emit_papra_write_gate_event_logs_three_fields) but the
doc count was not updated. Off-by-2.

This commit updates both lines to "15 cases" to match the
actual test inventory. The 7-bullet list above (attachment
collection, four rule outcomes, HTML body stripping,
classifier-order precedence, dry-run mode, env parsing,
is_configured()) is unchanged — the list still represents
the policy-level coverage, not the test-function count.

---ci---
project: inboxos
phase: 1
milestone: v1.3
status: execute
tasks_completed: [T2.3]
candidates_closed: [REQ-INB-31]
files_touched:
  - docs/papra-write-policy.md (2 lines, 192 and 202)
---/ci---

docs/papra-write-policy.md

@@ -189,7 +189,7 @@ Papra failures are **non-fatal**:
 
 ## Tests
 
-`pipelines/_tests/test_papra_decide_offline.py` covers 13 cases:
+`pipelines/_tests/test_papra_decide_offline.py` covers 15 cases:
 
 - attachment collection (inline images skipped, real PDFs found)
 - the four rule outcomes (attachment, body, metadata-only, default)
@@ -199,4 +199,4 @@ Papra failures are **non-fatal**:
 - env parsing for `PAPRA_DRY_RUN` and the module lists
 - `is_configured()` returns `False` when any of base_url / token / org is empty
 
-All 13 cases pass on the test environment.
+All 15 cases pass on the test environment.