docs: rename self-references from "LLM Wiki" to "memex"

Replace project self-references throughout README, SETUP, and the example
CLAUDE.md files. External artifact titles are preserved as-is since they
refer to the actual title of the Claude design artifact.

Also add a "Why 'memex'?" aside to the README that roots the project in
Vannevar Bush's 1945 "As We May Think" essay, where the term originates.
The compounding knowledge wiki is the LLM-era realization of Bush's
memex concept: the "associative trails" he imagined are the related:
frontmatter fields and wikilinks the agent maintains.

Kept lowercase where referring to the generic pattern (e.g. "an LLM wiki
persists its mistakes") since that refers to the class of system, not
this specific project.

docs/examples/wiki-CLAUDE.md

@@ -1,9 +1,10 @@
-# LLM Wiki — Schema
+# memex — Schema
 
-This is a persistent, compounding knowledge base maintained by LLM agents.
-It captures the **why** behind patterns, decisions, and implementations —
-not just the what. Copy this file to the root of your wiki directory
-(i.e. `~/projects/wiki/CLAUDE.md`) and edit for your own conventions.
+This is a persistent, compounding knowledge base maintained by LLM
+agents. It captures the **why** behind patterns, decisions, and
+implementations — not just the what. Copy this file to the root of your
+wiki directory (i.e. `~/projects/wiki/CLAUDE.md`) and edit for your own
+conventions.
 
 > This is an example `CLAUDE.md` for the wiki root. The agent reads this
 > at the start of every session when working inside the wiki. It's the