fix(serve): wire ContentSanitizer and ML classifier pipeline into zeph serve sessions

[bug-ops]

Summary

• src/serve/agent_factory.rs built every /sessions* Agent (the zeph serve HTTP/SSE path — the entry point most exposed to untrusted external input, spec-068 §9) without any of the ContentSanitizer pipeline (quarantine, guardrail, PII classifier/NER, three-class classifier, causal-IPI analyzer, NLI sanitizer, Vigil, secret masking) and without the ML injection classifier or [classifiers].enforcement_mode, even though src/runner.rs, src/daemon.rs, and src/acp.rs all applied this pipeline already. An operator who enabled hardening config ([security.vigil], [classifiers], secret masking, NLI, etc.) believing it covered every channel silently got none of it on Telegram/Discord/Slack sessions.
• Mirrors src/acp.rs's spawn_acp_agent: snapshots the same sanitizer/classifier config and resolved providers into ServeAgentDeps during assemble_serve_deps, then wires them onto each session's Agent in build_agent_factory using the same _with_cfg helpers and ordering (enforcement-mode after the injection classifier; secret-masking last, since it retroactively wraps every already-set provider field).
• Widens 9 SharedAgentDeps fields in src/acp.rs to pub(crate) (visibility-only) and adds a parity regression test (acp::tests::build_combined_deps_wires_equivalent_security_pipeline_from_config) driving build_combined_deps against a non-default security config, asserting both ServeAgentDeps and SharedAgentDeps reflect the configured values.

Closes #6580
Closes #6582

Test plan

• cargo +nightly fmt --check
• cargo clippy --profile ci --workspace --all-targets --features "desktop,ide,server,chat,pdf,scheduler,testing" -- -D warnings
• cargo nextest run --config-file .github/nextest.toml --workspace --features "desktop,ide,server,chat,pdf,scheduler" --lib --bins — 14879 passed, 36 skipped, 0 failures
• RUSTFLAGS="-D warnings" RUSTDOCFLAGS="--deny rustdoc::broken_intra_doc_links" cargo doc --no-deps --workspace --features "desktop,ide,server,chat,pdf,scheduler"
• gitleaks protect --staged
• CHANGELOG.md updated under [Unreleased]
• .local/testing/playbooks/wire-x-acp-daemon-serve-6580-6582.md added with concrete scenarios
• .local/testing/coverage-status.md row added (status: Untested — pending a live zeph serve-sessions verification pass in a future CI session)
• Live-session verification against a running zeph serve-sessions (playbook scenarios) — tracked separately per project convention, not required to land this fix