v3.11.0 — new service piston + whole-package security pass

Minor release. Adds engineer-man/piston as a new aigate service
(sandboxed multi-language code execution; nsjail-based per-execution
isolation; pre-bake architecture for runtime no-outbound), plus the
fallout from a full brutal-review pass across every line of code,
every doc, every config.

PISTON
  - 50+ languages available; default pre-bake is python + node only.
  - Pre-baked at image build time -> runtime container lives on
    aigate-internal ONLY (no outbound).
  - privileged:true is what piston needs to set up nsjail; the
    sandbox is the nsjail subprocess (own user ns, chroot, seccomp,
    cgroups). For aigate's threat model (trusted operator +
    bearer-auth-gated endpoint + sandboxed code from LLM agents)
    this is acceptable.
  - /piston/ nginx gate with `Bearer ${AIGATE_TOKEN}`; client
    Authorization header stripped before proxy hop.
  - MCP tool `mcp_tools-execute_code` exposed via the existing /mcp/
    aggregator.

SECURITY HARDENING
  - SSRF guard on llamacpp image_url fetches (both default path +
    Surya PDF path). Blocks RFC1918 / loopback / link-local /
    multicast / reserved hosts. Live-verified.
  - no-new-privileges:true added to claudebox, pibox-zai, ollama,
    ollama-cuda. README claim qualified for the two genuine
    carve-outs (piston needs privileged for nsjail; tailscale needs
    NET_ADMIN).
  - resource_manager: try/except BaseException wrapping the unload
    phase releases the semaphore on cancel; talkies CPU+CUDA unload
    lists synced to provider YAML (CPU 4->6, CUDA 8->14) so previously
    un-evicted models actually free memory under contention.

BUG FIXES
  - litellm/config/fallbacks.json: 20+ dead local-speaches-* / 4 dead
    local-qwen3-cuda-tts entries rewritten to live talkies slugs.
  - mcp/server.py: search_web num_results capped at 100;
    execute_code description no longer lies about installed
    runtimes.

DOCS
  - README Piper/Speaches drift cleaned (5 places).
  - new docs/services/piston.md.
  - 7 broken relative links in docs/services/* repaired.
  - docs/services-reference.md + docs/usage.md deleted (stale
    redirect stubs from v3.10.0).
  - docs/services/resource-management.md moved out of services/
    (it's cross-cutting LiteLLM callback logic, not a service).

TESTS
  - tests/test_piston.sh: 8 cases including
    test_piston_e2e_groq_drives_execute_code which exercises the
    full agentic loop (Groq llama-3.3-70b -> tool_call -> MCP ->
    piston nsjail -> SHA-256 verified byte-for-byte). All green.

Full per-file breakdown in CHANGELOG.md.