feat(tests): Add comprehensive tests for SSR admin vendors module

Add 8 BDD-style tests for the vendors module covering grid/list
operations and vendor merge functionality. Tests follow established
patterns from accounts_test.clj and include proper database
verification.

Tests Implemented:
- vendor-grid-loads-with-empty-database
- vendor-fetch-ids-returns-correct-structure
- vendor-fetch-page-returns-vendors
- vendor-hydrate-results-works
- vendor-merge-transfers-references
- vendor-merge-same-vendor-rejected
- vendor-merge-invalid-vendor-handled
- vendor-hydration-includes-all-fields

Key Implementation Details:
- Uses setup-test-data helper with unique temp IDs
- Tests focus on public interface (fetch-page, merge-submit)
- Follows BDD Given/When/Then pattern
- All 8 tests passing (26 assertions)

Documentation:
- Created implementation plan in docs/plans/
- Documented solution patterns in docs/solutions/
- Created code review todos for future improvements

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

todos/010-pending-p2-replace-create-vendor-helper.md

@@ -0,0 +1,172 @@
+---
+status: pending
+priority: p2
+issue_id: "010"
+tags: [testing, helpers, refactoring, vendors, dry]
+dependencies: []
+---
+
+# Replace Custom create-vendor Helper with test-vendor from util.clj
+
+## Problem Statement
+
+The vendors_test.clj defines a custom `create-vendor` helper (lines 18-25) that duplicates functionality already provided by `test-vendor` in `integration/util.clj`. This:
+- Violates DRY principle
+- Creates maintenance burden (two sources of truth)
+- May diverge over time
+
+## Findings
+
+**From architecture-strategist and kieran-rails-reviewer:**
+
+**Current custom helper (lines 18-25):**
+```clojure
+(defn create-vendor
+  "Create a vendor with a unique temp id"
+  [name & {:as attrs}]
+  (merge
+   {:db/id (str "vendor-" (java.util.UUID/randomUUID))
+    :vendor/name name
+    :vendor/default-account "test-account-id"}
+   attrs))
+```
+
+**Existing utility (util.clj lines 41-44):**
+```clojure
+(defn test-vendor [& kwargs]
+  (apply assoc {:db/id            "vendor-id"
+                :vendor/name      "Vendorson"
+                :vendor/default-account "test-account-id"}
+         kwargs))
+```
+
+**Usage comparison:**
+```clojure
+;; Current (vendors_test.clj):
+(create-vendor "Test Vendor 1")
+
+;; Could be (using test-vendor):
+(test-vendor :vendor/name "Test Vendor 1")
+```
+
+**Note:** The only difference is `create-vendor` generates unique IDs while `test-vendor` uses static ID. For unique IDs, can use:
+```clojure
+(assoc (test-vendor :vendor/name "Test") :db/id (str "vendor-" (UUID/randomUUID)))
+```
+
+## Proposed Solutions
+
+### Option A: Use test-vendor Directly (Recommended)
+**Effort:** Small (15 minutes)
+**Risk:** Low
+
+Remove `create-vendor` and use `test-vendor` with assoc for unique IDs:
+```clojure
+;; Instead of:
+(setup-test-data [(create-vendor "Test Vendor 1")])
+
+;; Use:
+(setup-test-data [(test-vendor :vendor/name "Test Vendor 1")])
+
+;; For unique IDs:
+(setup-test-data [(assoc (test-vendor :vendor/name "Test Vendor 1")
+                          :db/id (str "vendor-" (UUID/randomUUID)))])
+```
+
+**Pros:**
+- Single source of truth
+- Follows existing util.clj pattern
+- Removes duplication
+
+**Cons:**
+- More verbose for unique ID cases
+- Need to import UUID
+
+### Option B: Enhance test-vendor in util.clj
+**Effort:** Small (10 minutes)
+**Risk:** Low
+
+Modify `test-vendor` to auto-generate unique IDs:
+```clojure
+(defn test-vendor [& kwargs]
+  (apply assoc {:db/id (str "vendor-" (java.util.UUID/randomUUID))
+                :vendor/name "Vendorson"
+                :vendor/default-account "test-account-id"}
+         kwargs))
+```
+
+Then vendors_test.clj simply calls `(test-vendor :vendor/name "Test")`.
+
+**Pros:**
+- Improves utility for all test files
+- No local helper needed
+
+**Cons:**
+- May break existing tests expecting static ID
+- Requires updating util.clj (affects all tests)
+
+### Option C: Create Named Vendor Helper
+**Effort:** Small (5 minutes)
+**Risk:** Low
+
+Keep local helper but use test-vendor internally:
+```clojure
+(defn vendor-with-name [name]
+  (test-vendor :vendor/name name))
+```
+
+**Pros:**
+- Shorter than test-vendor call
+- Uses existing utility
+
+**Cons:**
+- Still have local helper
+- Less explicit than using test-vendor directly
+
+## Recommended Action
+
+**Go with Option A** - use `test-vendor` directly:
+1. Remove `create-vendor` helper
+2. Update all usages to use `test-vendor`
+3. Use `assoc` for unique IDs where needed
+
+This follows DRY principle and uses established patterns.
+
+## Technical Details
+
+**Affected Code:**
+- Lines 18-25: Remove `create-vendor` function
+- Lines 43-44, 58-59, 75-76, 98-101, etc.: Replace usages
+
+**Files:**
+- `test/clj/auto_ap/ssr/admin/vendors_test.clj`
+
+**Verification:**
+```bash
+lein test auto-ap.ssr.admin.vendors-test
+lein cljfmt check
+```
+
+## Acceptance Criteria
+
+- [ ] `create-vendor` helper removed
+- [ ] All usages replaced with `test-vendor`
+- [ ] Unique IDs handled with `assoc` where needed
+- [ ] Tests pass
+- [ ] Code formatted with lein cljfmt
+
+## Work Log
+
+### 2026-02-07 - Initial Creation
+
+**By:** Architecture Strategist Agent
+
+**Actions:**
+- Identified duplicate helper function
+- Compared with existing test-vendor utility
+- Documented usage patterns
+
+**Learnings:**
+- DRY principle violation in test helpers
+- test-vendor already provides same functionality
+- Small duplication can create maintenance burden