docs+feat: comprehensive local LLM provider guides and context length warning (#4294)

* docs: update llama.cpp section with --jinja flag and tool calling guide

The llama.cpp docs were missing the --jinja flag which is required for
tool calling to work. Without it, models output tool calls as raw JSON
text instead of structured API responses, making Hermes unable to
execute them.

Changes:
- Add --jinja and -fa flags to the server startup example
- Replace deprecated env vars (OPENAI_BASE_URL, LLM_MODEL) with
  hermes model interactive setup
- Add caution block explaining the --jinja requirement and symptoms
- List models with native tool calling support
- Add /props endpoint verification tip

* docs+feat: comprehensive local LLM provider guides and context length warning

Docs (providers.md):
- Rewrote Ollama section with context length warning (defaults to 4k on
  <24GB VRAM), three methods to increase it, and verification steps
- Rewrote vLLM section with --max-model-len, tool calling flags
  (--enable-auto-tool-choice, --tool-call-parser), and context guidance
- Rewrote SGLang section with --context-length, --tool-call-parser,
  and warning about 128-token default max output
- Added LM Studio section (port 1234, context length defaults to 2048,
  tool calling since 0.3.6)
- Added llama.cpp context length flag (-c) and GPU offload (-ngl)
- Added Troubleshooting Local Models section covering:
  - Tool calls appearing as text (with per-server fix table)
  - Silent context truncation and diagnosis commands
  - Low detected context at startup
  - Truncated responses
- Replaced all deprecated env vars (OPENAI_BASE_URL, LLM_MODEL) with
  hermes model interactive setup and config.yaml examples
- Added deprecation warning for legacy env vars in General Setup

Code (cli.py):
- Added context length warning in show_banner() when detected context
  is <= 8192 tokens, with server-specific fix hints:
  - Ollama (port 11434): suggests OLLAMA_CONTEXT_LENGTH env var
  - LM Studio (port 1234): suggests model settings adjustment
  - Other servers: suggests config.yaml override

Tests:
- 9 new tests covering warning thresholds, server-specific hints,
  and no-warning cases

cli.py

@@ -2192,7 +2192,31 @@ class HermesCLI:
         
         # Show tool availability warnings if any tools are disabled
         self._show_tool_availability_warnings()
-        
+
+        # Warn about very low context lengths (common with local servers)
+        if ctx_len and ctx_len <= 8192:
+            self.console.print()
+            self.console.print(
+                f"[yellow]⚠️  Context length is only {ctx_len:,} tokens — "
+                f"this is likely too low for agent use with tools.[/]"
+            )
+            self.console.print(
+                "[dim]   Hermes needs 16k–32k minimum. Tool schemas + system prompt alone use ~4k–8k.[/]"
+            )
+            base_url = getattr(self, "base_url", "") or ""
+            if "11434" in base_url or "ollama" in base_url.lower():
+                self.console.print(
+                    "[dim]   Ollama fix: OLLAMA_CONTEXT_LENGTH=32768 ollama serve[/]"
+                )
+            elif "1234" in base_url:
+                self.console.print(
+                    "[dim]   LM Studio fix: Set context length in model settings → reload model[/]"
+                )
+            else:
+                self.console.print(
+                    "[dim]   Fix: Set model.context_length in config.yaml, or increase your server's context setting[/]"
+                )
+
         self.console.print()
 
     def _preload_resumed_session(self) -> bool: