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/terminal_tool.py

@@ -1805,7 +1805,8 @@ def terminal_tool(
                 pass
             
             # Truncate output if too long, keeping both head and tail
-            MAX_OUTPUT_CHARS = 50000
+            from tools.tool_output_limits import get_max_bytes
+            MAX_OUTPUT_CHARS = get_max_bytes()
             if len(output) > MAX_OUTPUT_CHARS:
                 head_chars = int(MAX_OUTPUT_CHARS * 0.4)  # 40% head (error messages often appear early)
                 tail_chars = MAX_OUTPUT_CHARS - head_chars  # 60% tail (most recent/relevant output)