query: peg-based query language for ad-hoc graph exploration

poc-memory query "degree > 15"
poc-memory query "key ~ 'journal.*' AND degree > 10"
poc-memory query "neighbors('identity.md') WHERE strength > 0.5"
poc-memory query "community_id = community('identity.md')" --fields degree,category

Grammar-driven: the peg definition IS the language spec. Supports
boolean logic (AND/OR/NOT), numeric and string comparison, regex
match (~), graph traversal (neighbors() with WHERE), and function
calls (community(), degree()). Output flags: --fields, --sort,
--limit, --count.

New dependency: peg 0.8 (~68KB, 2 tiny deps).

Cargo.lock

@@ -932,6 +932,33 @@ version = "1.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "57c0d7b74b563b49d38dae00a0c37d4d6de9b432382b2892f0574ddcae73fd0a"
 
+[[package]]
+name = "peg"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9928cfca101b36ec5163e70049ee5368a8a1c3c6efc9ca9c5f9cc2f816152477"
+dependencies = [
+ "peg-macros",
+ "peg-runtime",
+]
+
+[[package]]
+name = "peg-macros"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6298ab04c202fa5b5d52ba03269fb7b74550b150323038878fe6c372d8280f71"
+dependencies = [
+ "peg-runtime",
+ "proc-macro2",
+ "quote",
+]
+
+[[package]]
+name = "peg-runtime"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "132dca9b868d927b35b5dd728167b2dee150eb1ad686008fc71ccb298b776fca"
+
 [[package]]
 name = "pest"
 version = "2.8.6"
@@ -991,6 +1018,8 @@ dependencies = [
  "faer",
  "libc",
  "memmap2",
+ "peg",
+ "rayon",
  "regex",
  "rkyv",
  "serde",