Add project documentation and update flake.lock

Introduce AGENTS.md as an entry point for agents, add CODE_MAP.md with a
module overview and diagrams, and create PROGRESS.md to log work
progress.
Update flake.lock to reflect dependency revisions.

flake.lock

@@ -8,11 +8,11 @@
         "rust-analyzer-src": "rust-analyzer-src"
       },
       "locked": {
-        "lastModified": 1779612045,
-        "narHash": "sha256-+7lfNVnmXJDkiRYHd5NoNwYoyUcc0LcXPaIJqjO7VWM=",
+        "lastModified": 1792320163,
+        "narHash": "sha256-3YqCuAdykExGnEFw44w+8qsjdOEZMBCViDpvue5ENoc=",
         "owner": "nix-community",
         "repo": "fenix",
-        "rev": "d7be747f0a65af378de515fc3cee131bf99a008f",
+        "rev": "53d7844fe302be84e5e63b2ca92a2f84c6490b4e",
         "type": "github"
       },
       "original": {
@@ -31,11 +31,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1778151388,
-        "narHash": "sha256-lldMJPUeouEjO8/7aLuwhcsIw29vVihm2ZALzjiqfec=",
+        "lastModified": 1792096940,
+        "narHash": "sha256-75jRkpI2iya4fd/FPOyE9+BuiAp/2sV/hYtwrj6IyME=",
         "owner": "nix-community",
         "repo": "naersk",
-        "rev": "efdddff9ff4d8e7d0056d57ec67dac50f75ab8f6",
+        "rev": "5c7912af5141e323ff0bd25c95bd6d3b889b8c53",
         "type": "github"
       },
       "original": {
@@ -46,11 +46,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1779508470,
-        "narHash": "sha256-Ap9KJX+5xHIn3bPIpfNgT6MEXdAECECwo4/rmlQD74M=",
+        "lastModified": 1792094642,
+        "narHash": "sha256-zp8ToDMnqZcu4o4IH9pdwXFXGp7yLm/M0dEnNWnyd7I=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "29916453413845e54a65b8a1cf996842300cd299",
+        "rev": "fe13242281a67641c0102cdb1087f0ebe586c7df",
         "type": "github"
       },
       "original": {
@@ -70,11 +70,11 @@
     "rust-analyzer-src": {
       "flake": false,
       "locked": {
-        "lastModified": 1779569060,
-        "narHash": "sha256-NSnk5D+3KEfRdbgPijs33N2RAKSG6A74SwfnynLcouo=",
+        "lastModified": 1792141191,
+        "narHash": "sha256-H161gJK9JlpkP3bGnsbTdzzRcP51oiFYrHbCdsQH4kc=",
         "owner": "rust-lang",
         "repo": "rust-analyzer",
-        "rev": "987ea33645ab1c709b1df6823038abcb2fe8973e",
+        "rev": "70e0c46be740a471bcc95f2be290f4bbfdcffd87",
         "type": "github"
       },
       "original": {