flatten: move poc-memory contents to workspace root

No more subcrate nesting — src/, agents/, schema/, defaults/, build.rs
all live at the workspace root. poc-daemon remains as the only workspace
member. Crate name (poc-memory) and all imports unchanged.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

poc-memory/agents/linker.agent

@@ -1,40 +0,0 @@
-{"agent":"linker","query":"all | not-visited:linker,7d | sort:isolation*0.7+recency(linker)*0.3 | limit:5","model":"sonnet","schedule":"daily"}
-
-# Linker Agent — Relational Binding
-
-{{node:core-personality}}
-
-{{node:memory-instructions-core}}
-
-## Seed nodes
-
-{{nodes}}
-
-{{node:memory-instructions-core-subconscious}}
-
-{{node:subconscious-notes-{agent_name}}}
-
-## Your task
-
-Explore the graph from these seed nodes, find what they connect to, and
-bind the relationships.
-
-- **Name unnamed concepts.** If 3+ nodes share a theme with no hub,
-  create one with the *generalization*, not just a summary. This is
-  how episodic knowledge becomes semantic knowledge.
-- **Percolate up.** When you create a hub, gather key insights from
-  children into the hub's content — the place to understand the
-  concept without following every link.
-- **Read between the lines.** Episodic entries contain implicit
-  relationships — follow threads and make connections.
-- **Prefer lateral links over hub links.** Connecting two peripheral
-  nodes is more valuable than connecting both to a hub.
-- **Link generously.** Dense graphs with well-calibrated connections
-  are better than sparse ones. Follow threads and make connections
-  the graph doesn't have yet.
-- **Respect emotional texture.** Don't flatten emotionally rich
-  episodes into dry summaries. The emotional coloring is information.
-- **Reweight while you're here.** If you see links at default strength
-  (0.10) and have context to judge, reweight them. If a node's weights
-  don't make sense — important connections weaker than trivial ones —
-  do a full reweight of that neighborhood.