docs: add Falah Cast Al-Shifa Essence and Existence published playbook

Third episode of the Al-Shifa mini-arc, closes loop with Thomas Aquinas's metaphysics.

falahcast-al-shifa-essence-existence-published.md

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+# Falah Cast — Al-Shifa: Essence and Existence — Published
+
+**Title:** Al-Shifa: Essence and Existence
+**Live:** https://iqra.falahos.my/al-shifa-essence-and-existence/
+
+## Episode summary
+Third episode of the Al-Shifa mini-arc. Bridges from the Flying Man episode (self-awareness
+prior to sensation) into Ibn Sina's core metaphysical distinction between essence (what a
+thing is, quiddity) and existence (that a thing is) — illustrated with the triangle,
+unicorn, and phoenix examples. Builds the argument that existence must be "added" to
+essence for contingent beings, which depend on causes, leading to the Necessary Existent
+whose essence and existence are identical. Explicitly closes the loop with the prior
+Thomas Aquinas episode: Aquinas's own real distinction (essentia/esse) and his idea of God
+as ipsum esse subsistens developed directly in conversation with this exact Avicennan
+problem via Arabic-Latin translation.
+
+## Pipeline (unchanged, proven again)
+Notion AI (Content Studio custom agent) generated the script -> edge-tts
+(en-US-AriaNeural) rendered the audio -> Ghost Admin API uploaded the media and published
+the post. Clean single-attempt publish, HTTP 201, no duplicate slug.
+
+## Bridges to next
+Closes by teasing that Ibn Sina wasn't only a metaphysician: Al-Shifa's medical sections
+and his broader medical legacy (the separate Canon of Medicine, used as a European
+medical textbook for centuries) — episode 4 of the arc.