Fix silent reinforcement: recognize [SILENT] token

[pbranchu]

Summary

• Add [SILENT] and [silent] to the NO_REPLY detection conditions in both streaming and non-streaming agent loop paths
• When the agent outputs these tokens, store [no reply needed] in history instead of the literal [SILENT] text, which would otherwise reinforce silence in future turns
• Fix pre-existing CI issues (clippy lints, test compilation, formatting)

Test plan

• Verify cargo fmt, clippy, and tests pass in CI
• Send a message where the agent should stay silent; verify [SILENT] is not stored literally in session history
• Verify NO_REPLY token still works as before
• Verify [[silent]] directive parsing still works as before

🤖 Generated with Claude Code

[jaberjaber23]

Reviewed. Three issues before merge:

1. Case sensitivity gap: the check matches [SILENT] and [silent] but misses [Silent] or other mixed-case variants that LLMs produce. Use .to_lowercase() for the comparison.

2. No unit tests for the new [SILENT] detection. Add tests asserting that [SILENT], [silent], and [Silent] all route to the no-reply path and store "[no reply needed]" in session history.

3. The openssl-src addition in Cargo.lock is unexplained and unrelated to this feature. Please explain or remove from this PR.