fix(config): validate unknown fields in LogConfig and warn in ParserConfig

[r266-tech]

Problem

Config file validation silently ignores unknown fields, causing subtle misconfigurations where users accidentally misspell field names (e.g. instead of ) without any warning.

Reported in #855

Root Cause

Two gaps in config validation:

1. LogConfig (Pydantic model) — Missing extra='forbid'. In Pydantic v2, the default is extra='ignore', which silently drops unknown fields.

2. ParserConfig (dataclass) — from_dict() filters unknown fields without any notification.

Fix

1. LogConfig — Added model_config = {extra: forbid}. Now raises a clear ValidationError listing the unknown field when a user writes e.g. log_level instead of level.

2. ParserConfig.from_dict() — Now logs a warning for each unknown field with 'did you mean?' suggestions via difflib. For example:

   • Unknown config field 'dimention' in EmbeddingModelConfig — did you mean 'dimension'?
   • Unknown config field 'max_concurent' in SomeConfig — ignoring

Testing

# LogConfig rejects unknown fields
LogConfig(level='DEBUG', typo_field='test')
# → pydantic.ValidationError: Extra inputs are not permitted

# ParserConfig warns about unknown fields
PDFConfig.from_dict({strategy: auto, typo_field: test})
# → WARNING: Unknown config field 'typo_field' in PDFConfig — ignoring

Why warning for dataclass configs?

Parser configs use Python dataclasses (not Pydantic), so we can't use extra='forbid'. A warning approach is less disruptive while still surfacing the problem. The LogConfig fix (strict error) provides the hard rejection the reporter requested for Pydantic-based configs.

[github-actions]

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