Add unit_primitives field for locally define prompts

What does this MR do and why?

I discovered that in the current AI catalog flow's flow_v2 version (app/validators/json_schemas/ai_catalog/flow_v2.json), unit_primitives is not included for locally defined prompts. Instead, it is part of the model object. This MR adds unit_primitives as an optional field under the prompts object and removes it from the model component. For reference, see the flow register v1 example.

version: "v1"
environment: ambient

components:
    - name: "code_analyzer"
      type: AgentComponent
      prompt_id: "my_local_prompt"
      # prompt_version omitted - uses local prompt
      ui_log_events: [ "on_agent_final_answer" ]
      inputs: ["context:goal"]
      toolset: ["read_file", "list_dir"]

prompts:
    - prompt_id: "my_local_prompt"
      name: "Code Analysis Assistant"
      model:
        params:
            model_class_provider: anthropic
            model: claude-sonnet-4-20250514
            max_tokens: 32_768
      unit_primitives: []
      prompt_template:
          system: "You are a helpful assistant specialized in code analysis"
          user: "{{goal}}"
          placeholder: history  # Optional: include conversation history
      params:
          timeout: 180

routers:
    - from: "code_analyzer"
      to: "end"

flow:
    entry_point: "code_analyzer"

Note: Currently, there are no flow records in production, as this feature is behind a feature flag set to false by default.

 Index Scan using index_ai_catalog_items_on_item_type on public.ai_catalog_items  (cost=0.15..3.17 rows=1 width=273) (actual time=0.022..0.023 rows=0 loops=1)
   Index Cond: (ai_catalog_items.item_type = 2)
   Buffers: shared hit=4
   I/O Timings: read=0.000 write=0.000
Settings: seq_page_cost = '4', work_mem = '100MB', random_page_cost = '1.5', jit = 'off', effective_cache_size = '472585MB'

References

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Before	After

How to set up and validate locally

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Related to #578228