feat: add TOML site config for metadata

- Cargo.toml: Add toml and serde dependencies
- site.toml: New config with title, author, base_url
- src/config.rs: SiteConfig struct with load() function
- src/error.rs: Add Error::Config for parse errors
- src/main.rs: Load site.toml, thread config and page paths
  through generators
- src/templates.rs: Use config.title in nav/titles,
  config.author in footer, config.base_url for canonical URLs.

All three config fields verified in generated HTML output.

Cargo.lock

@@ -326,7 +326,7 @@ checksum = "8666976c40b8633f918783969b6681a3ddb205f29150348617de425d85a3e3bd"
 dependencies = [
  "serde",
  "serde_json",
- "toml",
+ "toml 0.5.11",
  "yaml-rust2",
 ]
 
@@ -510,7 +510,9 @@ dependencies = [
  "lightningcss",
  "maud",
  "pulldown-cmark",
+ "serde",
  "thiserror 2.0.18",
+ "toml 0.8.23",
  "tree-sitter-bash",
  "tree-sitter-highlight",
  "tree-sitter-json",
@@ -931,6 +933,15 @@ dependencies = [
  "zmij",
 ]
 
+[[package]]
+name = "serde_spanned"
+version = "0.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bf41e0cfaf7226dca15e8197172c295a782857fcb97fad1808a166870dee75a3"
+dependencies = [
+ "serde",
+]
+
 [[package]]
 name = "shlex"
 version = "1.3.0"
@@ -1062,6 +1073,47 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "toml"
+version = "0.8.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc1beb996b9d83529a9e75c17a1686767d148d70663143c7854d8b4a09ced362"
+dependencies = [
+ "serde",
+ "serde_spanned",
+ "toml_datetime",
+ "toml_edit",
+]
+
+[[package]]
+name = "toml_datetime"
+version = "0.6.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22cddaf88f4fbc13c51aebbf5f8eceb5c7c5a9da2ac40a13519eb5b0a0e8f11c"
+dependencies = [
+ "serde",
+]
+
+[[package]]
+name = "toml_edit"
+version = "0.22.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41fe8c660ae4257887cf66394862d21dbca4a6ddd26f04a3560410406a2f819a"
+dependencies = [
+ "indexmap",
+ "serde",
+ "serde_spanned",
+ "toml_datetime",
+ "toml_write",
+ "winnow",
+]
+
+[[package]]
+name = "toml_write"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5d99f8c9a7727884afe522e9bd5edbfc91a3312b36a77b5fb8926e4c31a41801"
+
 [[package]]
 name = "tree-sitter"
 version = "0.24.7"
@@ -1264,6 +1316,15 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "winnow"
+version = "0.7.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a5364e9d77fcdeeaa6062ced926ee3381faa2ee02d3eb83a5c27a8825540829"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "wit-bindgen"
 version = "0.51.0"