[AZ-171] Add TensorRT tests, AC coverage gate in implement skill, optimize test infrastructure

- Add TensorRT export tests with graceful skip when no GPU available
- Add AC test coverage verification step (Step 8) to implement skill
- Add test coverage gap analysis to new-task skill
- Move exported_models fixture to conftest.py as session-scoped (shared across modules)
- Reorder tests: e2e training runs first so images/labels are available for all tests
- Consolidate teardown into single session-level cleanup in conftest.py
- Fix infrastructure tests to count files dynamically instead of hardcoded 20

Made-with: Cursor

.cursor/skills/new-task/SKILL.md

@@ -129,7 +129,7 @@ The `<task_slug>` is a short kebab-case name derived from the feature descriptio
 ### Step 4: Codebase Analysis
 
 **Role**: Software architect
-**Goal**: Determine where and how to insert the new functionality.
+**Goal**: Determine where and how to insert the new functionality, and whether existing tests cover the new requirements.
 
 1. Read the codebase documentation from DOCUMENT_DIR:
    - `architecture.md` — overall structure
@@ -144,6 +144,10 @@ The `<task_slug>` is a short kebab-case name derived from the feature descriptio
    - What new interfaces or models are needed
    - How data flows through the change
 4. If the change is complex enough, read the actual source files (not just docs) to verify insertion points
+5. **Test coverage gap analysis**: Read existing test files that cover the affected components. For each acceptance criterion from Step 1, determine whether an existing test already validates it. Classify each AC as:
+   - **Covered**: an existing test directly validates this behavior
+   - **Partially covered**: an existing test exercises the code path but doesn't assert the new requirement
+   - **Not covered**: no existing test validates this behavior — a new test is required
 
 Present the analysis:
 
@@ -156,9 +160,22 @@ Present the analysis:
  Interface changes:   [list or "None"]
  New interfaces:      [list or "None"]
  Data flow impact:    [summary]
+ ─────────────────────────────────────
+ TEST COVERAGE GAP ANALYSIS
+ ─────────────────────────────────────
+ AC-1: [Covered / Partially covered / Not covered]
+       [existing test name or "needs new test"]
+ AC-2: [Covered / Partially covered / Not covered]
+       [existing test name or "needs new test"]
+ ...
+ ─────────────────────────────────────
+ New tests needed:  [count]
+ Existing tests to update: [count or "None"]
 ══════════════════════════════════════
 ```
 
+When gaps are found, the task spec (Step 6) MUST include the missing tests in the Scope (Included) section and the Unit/Blackbox Tests tables. Tests are not optional — if an AC is not covered by an existing test, the task must deliver a test for it.
+
 ---
 
 ### Step 5: Validate Assumptions