feat(config): make tool output truncation limits configurable

Port from anomalyco/opencode#23770: expose a new `tool_output` config
section so users can tune the hardcoded truncation caps that apply to
terminal output and read_file pagination.

Three knobs under `tool_output`:
- max_bytes (default 50_000) — terminal stdout/stderr cap
- max_lines (default 2000) — read_file pagination cap
- max_line_length (default 2000) — per-line cap in line-numbered view

All three keep their existing hardcoded values as defaults, so behaviour
is unchanged when the section is absent. Power users on big-context
models can raise them; small-context local models can lower them.

Implementation:
- New `tools/tool_output_limits.py` reads the section with defensive
  fallback (missing/invalid values → defaults, never raises).
- `tools/terminal_tool.py` MAX_OUTPUT_CHARS now comes from
  get_max_bytes().
- `tools/file_operations.py` normalize_read_pagination() and
  _add_line_numbers() now pull the limits at call time.
- `hermes_cli/config.py` DEFAULT_CONFIG gains the `tool_output` section
  so `hermes setup` writes defaults into fresh configs.
- Docs page `user-guide/configuration.md` gains a "Tool Output
  Truncation Limits" section with large-context and small-context
  example configs.

Tests (18 new in tests/tools/test_tool_output_limits.py):
- Default resolution with missing / malformed / non-dict config.
- Full and partial user overrides.
- Coercion of bad values (None, negative, wrong type, str int).
- Shortcut accessors delegate correctly.
- DEFAULT_CONFIG exposes the section with the right defaults.
- Integration: normalize_read_pagination clamps to the configured
  max_lines.

tools/tool_output_limits.py

@@ -0,0 +1,92 @@
+"""Configurable tool-output truncation limits.
+
+Ported from anomalyco/opencode PR #23770 (``feat(truncate): allow
+configuring tool output truncation limits``).
+
+OpenCode hardcoded ``MAX_LINES = 2000`` and ``MAX_BYTES = 50 * 1024``
+as tool-output truncation thresholds. Hermes-agent had the same
+hardcoded constants in two places:
+
+* ``tools/terminal_tool.py`` — ``MAX_OUTPUT_CHARS = 50000`` (terminal
+  stdout/stderr cap)
+* ``tools/file_operations.py`` — ``MAX_LINES = 2000`` /
+  ``MAX_LINE_LENGTH = 2000`` (read_file pagination cap + per-line cap)
+
+This module centralises those values behind a single config section
+(``tool_output`` in ``config.yaml``) so power users can tune them
+without patching the source. The existing hardcoded numbers remain as
+defaults, so behaviour is unchanged when the config key is absent.
+
+Example ``config.yaml``::
+
+    tool_output:
+      max_bytes: 100000        # terminal output cap (chars)
+      max_lines: 5000          # read_file pagination + truncation cap
+      max_line_length: 2000    # per-line length cap before '... [truncated]'
+
+The limits reader is defensive: any error (missing config file, invalid
+value type, etc.) falls back to the built-in defaults so tools never
+fail because of a malformed config.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict
+
+# Hardcoded defaults — these match the pre-existing values, so adding
+# this module is behaviour-preserving for users who don't set
+# ``tool_output`` in config.yaml.
+DEFAULT_MAX_BYTES = 50_000       # terminal_tool.MAX_OUTPUT_CHARS
+DEFAULT_MAX_LINES = 2000         # file_operations.MAX_LINES
+DEFAULT_MAX_LINE_LENGTH = 2000   # file_operations.MAX_LINE_LENGTH
+
+
+def _coerce_positive_int(value: Any, default: int) -> int:
+    """Return ``value`` as a positive int, or ``default`` on any issue."""
+    try:
+        iv = int(value)
+    except (TypeError, ValueError):
+        return default
+    if iv <= 0:
+        return default
+    return iv
+
+
+def get_tool_output_limits() -> Dict[str, int]:
+    """Return resolved tool-output limits, reading ``tool_output`` from config.
+
+    Keys: ``max_bytes``, ``max_lines``, ``max_line_length``. Missing or
+    invalid entries fall through to the ``DEFAULT_*`` constants. This
+    function NEVER raises.
+    """
+    try:
+        from hermes_cli.config import load_config
+        cfg = load_config() or {}
+        section = cfg.get("tool_output") if isinstance(cfg, dict) else None
+        if not isinstance(section, dict):
+            section = {}
+    except Exception:
+        section = {}
+
+    return {
+        "max_bytes": _coerce_positive_int(section.get("max_bytes"), DEFAULT_MAX_BYTES),
+        "max_lines": _coerce_positive_int(section.get("max_lines"), DEFAULT_MAX_LINES),
+        "max_line_length": _coerce_positive_int(
+            section.get("max_line_length"), DEFAULT_MAX_LINE_LENGTH
+        ),
+    }
+
+
+def get_max_bytes() -> int:
+    """Shortcut for terminal-tool callers that only need the byte cap."""
+    return get_tool_output_limits()["max_bytes"]
+
+
+def get_max_lines() -> int:
+    """Shortcut for file-ops callers that only need the line cap."""
+    return get_tool_output_limits()["max_lines"]
+
+
+def get_max_line_length() -> int:
+    """Shortcut for file-ops callers that only need the per-line cap."""
+    return get_tool_output_limits()["max_line_length"]