Reject non-boolean replace_all plan values

[1x0f8]

Motivation

• The LLM plan schema treats replace_all as a boolean, but the local validatePlan did not enforce that type, allowing string values like "false" to be cast to true during execution and causing unintended global replacements.

Description

• Enforce that replace_all is a boolean in validatePlan to reject missing or non-boolean replace_text operations (file: src/Agent.php).
• Add a regression assertion to tests/smoke.php that validates a string-valued replace_all (e.g. 'false') is rejected by plan validation.

Testing

• Ran PHP lint across bin, config, public, src, and tests with php -l and there were no syntax errors.
• Executed the smoke test php tests/smoke.php which passed and includes the new assertion preventing non-boolean replace_all values.

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Codex Task