feat: add video OCR/ASR, DOCX/PDF export, input block and risk config updates

- Video pipeline: video file OCR via VLM plus audio track ASR, integrated
  into job_handlers with progress emit per phase. New media_utils.py for
  audio extraction from video files.
- Document export: richExport.js replaces inline docx builder; DOCX and PDF
  export buttons are now enabled in MilkdownEditor. File size limit raised to
  100 MB.
- Input block: new InputBlockCrepe.vue component with inputBlockPlugin.ts
  and inputBlock.js for custom user-input nodes in the editor.
- Risk config: added Vite dev server ports (5173) to CORS allowlist and
  increased OCR max input from 10 MB to 100 MB.
- TTS/ASR refactor: simplified tts_asr.py model loading and warmup logic.
- Test coverage: updated tests for llm, main endpoints, pro completions and
  web search modules.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/risk_config.py

@@ -92,7 +92,7 @@ class RiskConfig:
 def load_risk_config() -> RiskConfig:
     raw_origins = _str_env(
         "CORS_ALLOW_ORIGINS",
-        "https://chat.imageteach.tech,http://localhost:8080,http://127.0.0.1:8080",
+        "https://chat.imageteach.tech,http://localhost:8080,http://127.0.0.1:8080,http://localhost:5173,http://127.0.0.1:5173",
     )
     cors_allow_origins = tuple(
         origin.strip() for origin in raw_origins.split(",") if origin.strip()
@@ -138,7 +138,7 @@ def load_risk_config() -> RiskConfig:
         web_search_temperature=_float_env("RISK_WEB_SEARCH_TEMPERATURE", 0.4),
         compress_max_input_chars=_int_env("RISK_COMPRESS_MAX_INPUT_CHARS", 128000),
         compress_max_output_tokens=_int_env("RISK_COMPRESS_MAX_OUTPUT_TOKENS", 1536),
-        ocr_max_input_bytes=_int_env("RISK_OCR_MAX_INPUT_BYTES", 10 * 1024 * 1024),
+        ocr_max_input_bytes=_int_env("RISK_OCR_MAX_INPUT_BYTES", 100 * 1024 * 1024),
         completion_input_cost_per_1k=_float_env("RISK_COMPLETION_INPUT_COST_PER_1K", 0.0004),
         completion_output_cost_per_1k=_float_env("RISK_COMPLETION_OUTPUT_COST_PER_1K", 0.0016),
         pro_input_cost_per_1k=_float_env("RISK_PRO_INPUT_COST_PER_1K", 0.003),