Add Codex research skills and setup docs

Include Codex setup docs, installer updates, and switch the OpenCode web research agent default model to gpt-5.4.

skills/research-codex-en/research-add-fields/SKILL.md

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+---
+name: research-add-fields
+description: Add field definitions to existing research outline.
+---
+
+# Research Add Fields - Supplement Research Fields
+
+## Trigger
+`/research-add-fields`
+
+## Workflow
+
+### Step 1: Auto-locate Fields File
+Find `*/fields.yaml` file in current working directory, auto-read existing fields definitions.
+
+### Step 2: Get Supplement Source
+Ask user to choose:
+- **A. User direct input**: User provides field names and descriptions
+- **B. Web Search**: Launch agent to search common fields in this domain
+
+### Step 3: Display and Confirm
+- Display suggested new fields list
+- User confirms which fields to add
+- User specifies field category and detail_level
+
+### Step 4: Save Update
+Append confirmed fields to fields.yaml, save file.
+
+## Output
+Updated `{topic}/fields.yaml` file (in-place modification, requires user confirmation)