cli: extract graph commands from main.rs into cli/graph.rs

Move 18 graph subcommand handlers (594 lines) out of main.rs:
link, link-add, link-impact, link-audit, link-orphans,
triangle-close, cap-degree, normalize-strengths, differentiate,
trace, spectral-*, organize, interference.

main.rs: 3130 → 2518 lines.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

poc-memory/src/lib.rs

@@ -21,6 +21,9 @@ pub mod neuro;
 pub mod counters;
 pub mod cursor;
 
+// CLI handlers (split from main.rs)
+pub mod cli;
+
 // Agent layer (LLM-powered operations)
 pub mod agents;
 pub mod tui;