perf: fix translate deadlock, speed, trace_id, UI bugs — fullstack patch

## Backend (7 production files + 6 test files)

### P0-2: LLM output truncation cascade fix
- _token_budget.py: OUTPUT_PER_ROW_PER_LANG 120→200, OUTPUT_SAFETY_FACTOR 0.70→0.55
- Prevents finish_reason=length → split → retry cascade (3 calls → 1 call per batch)
- P2-8: added qwen-flash/qwen-plus/qwen-max/qwen-coder to PROVIDER_DEFAULTS

### P1-4/P1-5: EncryptionManager singleton
- encryption.py: get_encryption_manager() process-wide singleton
- llm_provider.py: use singleton instead of new EncryptionManager() per batch
- Eliminates ~90 redundant Fernet key validations per translation run

### P1-6: Cache-hit log aggregation
- _batch_proc.py: one log per batch (batch_rows + cache_hits) instead of per-row
- 1076 log lines → ~30 per run

### P1-7: Timezone-aware datetime fix
- scheduler.py: _ensure_aware() helper for naive DB datetime → UTC-aware
- Fixes TypeError in scheduled translation concurrency check

### P2-9: Connection test timeout
- connection_service.py: asyncio.wait_for(15s) on all dialect tests
- Prevents 2-minute UI hangs from DNS/TCP stalls

### Trace ID propagation
- middleware/trace.py: inject x-trace-id response header via ASGI send wrapper

### Test fixes & integration tests
- test_scheduler.py: AsyncMock for execute_run, mock get_async_job_runner
- test_sql_insert_service.py: AsyncMock for execute_sql
- test_token_budget.py: batch_size 50→45 for new OUTPUT_PER_ROW_PER_LANG=200
- test_encryption.py: +2 singleton tests
- test_scheduler_ensure_aware.py: +4 (naive→aware, passthrough, None, subtraction)
- test_batch_classify_persist.py: +2 cache-hit aggregation tests
- test_connection_service_edge.py: +2 timeout tests
- test_trace_middleware.py: +4 x-trace-id header tests
- test_token_budget.py: +4 qwen-flash/O200 tests

## Frontend (7 production files + 5 test files)

### Trace ID propagation
- api.ts: _captureTraceId() reads x-trace-id → setTraceId() in fetchApi/requestApi/postApi/deleteApi

### Duplicate datasource columns fetch
- ConfigTabForm.svelte: guard availableColumns.length === 0 before fetch

### Admin pages Svelte 5 runes fix
- admin/users/+page.svelte: plain let → () for all template-bound vars
- admin/roles/+page.svelte: same fix
- Both pages were stuck on «Загрузка...» due to mixed reactivity models

### Validation popover positioning
- +page.svelte: pass trigger HTMLElement instead of event
- DashboardHubModel.svelte.ts: toggleValidationPopover(HTMLElement), closeValidationPopover()
- Added X close button + click-outside overlay + i18n

### Test fixes & integration tests
- api.test.ts: mock setTraceId/getTraceId, +3 _captureTraceId tests
- provider_config.integration.test.ts: handleDelete→promptDeleteProvider
- DatasetPreview.test.ts: dashboards/ → ROUTES.dashboards
- test_config_tab_form.svelte.js: +2 columns fetch guard tests (NEW)
- admin-users.test.ts: +3 loading→table tests (NEW)
- admin-roles.test.ts: +2 loading→table tests (NEW)

## Semantic curation
- Removed @COMPLEXITY N from 6 route files + metrics.py (duplicate of [C:N])
- Added [C:N] to 2 orphan child contracts in metrics.py
- Added [C:N] + @BRIEF to 4 frontend anchors
- Fixed #region → # #region consistency in validation_tasks.py

## Verification
- Backend: 608 pytest passed (0 failures)
- Frontend: 2472 vitest passed (128 files, 0 failures)
- Frontend build: ✓ built in 18s
- Browser: dashboards, admin/users, admin/roles, validation popover — all green

backend/src/api/routes/translate/_correction_routes.py

@@ -66,7 +66,6 @@ async def submit_correction(
 # @POST All corrections applied or none with conflict list.
 # @SIDE_EFFECT Creates/updates DictionaryEntry rows; commits once.
 # @RELATION DEPENDS_ON -> [DictionaryManager]
-# @COMPLEXITY 4
 
 @router.post("/corrections/bulk")
 async def submit_bulk_corrections(

backend/src/api/routes/translate/_job_routes.py

@@ -204,7 +204,6 @@ async def duplicate_job(
 # @SIDE_EFFECT Queries Superset API for dataset detail and database info.
 # @RATIONALE Dialect detection from Superset connection cached on TranslationJob at save time.
 # @REJECTED Hardcoding dialect list per database — would drift from actual Superset config.
-# @COMPLEXITY 4
 
 @router.get("/datasources")
 async def list_datasources(

backend/src/api/routes/translate/_metrics_routes.py

@@ -47,7 +47,6 @@ async def get_metrics(
 # @BRIEF Get aggregated metrics for a specific job.
 # @PRE User has translate.metrics.view permission.
 # @POST Returns metrics dict.
-# @COMPLEXITY 4
 
 @router.get("/jobs/{job_id}/metrics")
 async def get_job_metrics(

backend/src/api/routes/translate/_run_list_routes.py

@@ -178,7 +178,6 @@ async def get_run_detail(
 # @BRIEF Download a CSV of skipped translation records from a run.
 # @PRE User has translate.job.view permission.
 # @POST Returns CSV file of skipped records.
-# @COMPLEXITY 4
 
 @router.get("/runs/{run_id}/skipped.csv")
 async def download_skipped_csv(

backend/src/api/routes/translate/_schedule_routes.py

@@ -216,7 +216,6 @@ async def delete_schedule(
 # @BRIEF Preview next N executions for a job's schedule.
 # @PRE User has translate.schedule.view permission.
 # @POST Returns next execution times.
-# @COMPLEXITY 4
 
 @router.get("/jobs/{job_id}/schedule/next-executions")
 async def get_next_executions(

backend/src/api/routes/validation_tasks.py

@@ -1,4 +1,4 @@
-#region ValidationTasksRoutes [C:4] [TYPE Module] [SEMANTICS fastapi, validation, api, task, run]
+# #region ValidationTasksRoutes [C:4] [TYPE Module] [SEMANTICS fastapi, validation, api, task, run]
 # @BRIEF API routes for validation task management — v2 CRUD with run history and Superset URL parsing.
 # @LAYER API
 # @RELATION DEPENDS_ON -> [ValidationTaskService]