feat(codex): migrate newsletter workflows to skills

.agents/skills/mt-add-image/SKILL.md

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+---
+name: mt-add-image
+description: Add an image URL to today's Hugo newsletter Bonus Images section with a detected or user-provided label. Use directly for a known image URL or when dispatched by mt-add-url.
+---
+
+# Add a newsletter image
+
+Read and follow `../../../.claude/skills/mt-add-image/SKILL.md` completely.
+
+Treat that file as the canonical workflow and resolve its relative paths from its own directory.

.agents/skills/mt-add-post/SKILL.md

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+---
+name: mt-add-post
+description: Add an article or blog URL to today's Hugo newsletter with its original title and a Vietnamese summary. Use directly for a known article URL or when dispatched by mt-add-url.
+---
+
+# Add a newsletter article
+
+Read and follow `../../../.claude/skills/mt-add-post/SKILL.md` completely.
+
+Treat that file as the canonical workflow and resolve its relative paths from its own directory.

.agents/skills/mt-add-tags/SKILL.md

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+---
+name: mt-add-tags
+description: Add or update Hugo post tags after analyzing the post. Use when the user asks to tag a post or before committing a post with empty or generic-only tags.
+---
+
+# Add newsletter tags
+
+Read and follow `../../../.claude/skills/mt-add-tags/SKILL.md` completely.
+
+Treat that file as the canonical workflow and resolve its relative paths from its own directory.

.agents/skills/mt-add-url/SKILL.md

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+---
+name: mt-add-url
+description: Meta entry for adding one or more URLs to the Hugo blog newsletter. Classifies each URL and dispatches articles, YouTube videos, and images to the matching handler. Use whenever the user asks to add URLs to a newsletter.
+---
+
+# Add newsletter URLs
+
+Read and follow `../../../.claude/skills/mt-add-url/SKILL.md` completely.
+
+Treat that file as the canonical workflow. Resolve every relative path it references from its own directory, including `references/newsletter-post-mechanics.md`.

.agents/skills/mt-add-video/SKILL.md

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+---
+name: mt-add-video
+description: Add a YouTube URL to today's Hugo newsletter Bonus Videos section with a Vietnamese title and summary. Use directly for a known YouTube URL or when dispatched by mt-add-url.
+---
+
+# Add a newsletter video
+
+Read and follow `../../../.claude/skills/mt-add-video/SKILL.md` completely.
+
+Treat that file as the canonical workflow and resolve its relative paths from its own directory.

.agents/skills/mt-webfetch/SKILL.md

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+---
+name: mt-webfetch
+description: Fetch public web content through the defuddle fallback only after the built-in fetch is blocked or returns unusable content. Do not use for paywalls, login walls, or as the first fetch attempt.
+---
+
+# Fetch blocked newsletter sources
+
+Read and follow `../../../.claude/skills/mt-webfetch/SKILL.md` completely.
+
+Treat that file as the canonical workflow and resolve its relative paths from its own directory.