server: Jinja chat template rendering via minijinja

Load the model's chat_template.jinja (or tokenizer_config.json
chat_template field) at startup and render it with minijinja instead of
hardcoded per-model prompt builders.

Custom Jinja functions: strftime_now (date formatting), raise_exception
(template validation errors).  Falls back to Qwen3 ChatML template if
no Jinja template is found.

Removes the hardcoded build_prompt_gpt_oss() — the model's own template
now drives prompt formatting, matching llama.cpp's behavior exactly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -408,12 +408,28 @@ version = "2.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8ca58f447f06ed17d5fc4043ce1b10dd205e060fb3ce5b979b8ed8e59ff3f79"
 
+[[package]]
+name = "memo-map"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38d1115007560874e373613744c6fba374c17688327a71c1476d1a5954cc857b"
+
 [[package]]
 name = "mime"
 version = "0.3.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6877bb514081ee2a7ff5ef9de3281f14a4dd4bceac4c09388074a6b5df8a139a"
 
+[[package]]
+name = "minijinja"
+version = "2.20.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2929e494b2280e1e18959bb2e121da03347ae896896fdfaceaab43c88a02803f"
+dependencies = [
+ "memo-map",
+ "serde",
+]
+
 [[package]]
 name = "mio"
 version = "1.2.0"
@@ -1097,6 +1113,14 @@ dependencies = [
  "rand 0.9.4",
 ]
 
+[[package]]
+name = "xserv-distributed"
+version = "0.1.0"
+dependencies = [
+ "half",
+ "xserv-cuda",
+]
+
 [[package]]
 name = "xserv-kernels"
 version = "0.1.0"
@@ -1112,12 +1136,14 @@ name = "xserv-model"
 version = "0.1.0"
 dependencies = [
  "half",
+ "libc",
  "rand 0.8.6",
  "safetensors",
  "serde",
  "serde_json",
  "smallvec",
  "xserv-cuda",
+ "xserv-distributed",
  "xserv-kernels",
  "xserv-tensor",
  "xserv-tokenizer",
@@ -1129,12 +1155,14 @@ version = "0.1.0"
 dependencies = [
  "axum",
  "half",
+ "minijinja",
  "serde",
  "serde_json",
  "tokio",
  "tokio-stream",
  "uuid",
  "xserv-cuda",
+ "xserv-distributed",
  "xserv-kernels",
  "xserv-model",
  "xserv-tensor",