Ember v0.5.1

Patch release on top of v0.5.0 (CI-green on the pinned Rust 1.92 toolchain).

Fixed

• CI clippy on Rust 1.92: src/v05/testutil.rs had a file-level
  #![cfg(test)] alongside the #[cfg(test)] module gate in mod.rs;
  rustc 1.92 rejects the duplicated attribute. Verified locally with
  cargo +1.92.0 clippy -- -D warnings and cargo +1.92.0 test --all-targets (237 + 19 + 46 + 5 tests green).
• Docs: docs/usage.md repointed the v0.2 activation-artifact schema
  reference from docs/experiments.md (now the v0.5 doc) to
  activation-artifacts.md / activation-patching.md.

Added

• Recorded capture-from-bundle real-model workflow (Gate D evidence)
  on Llama-3.2-1B-Instruct-Q8_0: baseline captures prompt-final
  attention-output across all layers; a second run replaces layer 8's
  row with the baseline bundle's layer-3 row; a third run adds
  restore-original. Results: layers 0-8 bit-exact, 9-15 diverge;
  restoration reproduces the baseline with all 16 capture layers exact
  and outputs equal. Specs/hashes under
  artifacts/benchmark-v05/capture-from-bundle/, commands in
  docs/interventions.md.
• Refreshed Gate H matrix with the release binary: ordinary runs
  2.58 s / 2,751,028 kB RSS vs 2.61 s / 2,751,024 kB with experiment
  machinery unused; experiment workloads +2.2% RSS (gate ≤3%).

Binaries: build from source (cargo build --release); no model files
are distributed.