ci(rust): add build/test/clippy gate; make the crates clippy-clean

The only Rust CI was CodeQL in build-mode `none` (buildless), so nothing
ever compiled or tested robot-repo-automaton / shared-context / dashboard
— which is how the non-compiling content-match path reached `main` before
it was fixed in the prior PR. Add `.github/workflows/rust.yml`: a per-crate
matrix running `cargo build --all-targets`, `cargo test`, and
`cargo clippy --all-targets -- -D warnings` (blocking), with
`cargo fmt --check` informational (there is pre-existing formatting drift —
~180 hunks — that is intentionally not gated yet).

To make the clippy gate pass, fix the existing findings:
- fixer.rs: drop a no-op `.replace("hyperpolymath", "hyperpolymath")`.
- registry_guard.rs: use `split_once('/')` instead of a manual `splitn(2)`.
- exclusion_registry.rs: rename the inherent `from_str` -> `parse` (it is
  not a `FromStr` impl; matches `Catalog::parse`) and use `if let Ok(..)`
  instead of `.ok()` + `if let Some(..)`.
- hypatia.rs / main.rs: accept `&Path` instead of `&PathBuf`.
- Cargo.toml (robot-repo-automaton + shared-context): drop the ignored
  `+spec-1.1.0` build metadata from the `toml` version requirement
  (resolution-neutral; silences the cargo warning).
- benches: import `std::hint::black_box` (criterion's re-export is deprecated).

All three crates are clippy `-D warnings` clean; 101 + 84 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RozeeLxpJsd3WWFngaZWz3

Author: claude

.github/workflows/rust.yml

@@ -0,0 +1,47 @@
+# SPDX-License-Identifier: MPL-2.0
+name: Rust
+# Build + test + clippy gate for the three standalone Rust crates.
+# Added after a non-compiling crate (robot-repo-automaton) reached `main`
+# unnoticed: the only prior Rust CI was CodeQL in build-mode `none`
+# (buildless), so nothing actually compiled or tested these crates.
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: ['**']
+permissions:
+  contents: read
+env:
+  CARGO_TERM_COLOR: always
+  # reqwest=rustls-tls, git2=vendored-openssl, gix=rust-tls. OPENSSL_NO_VENDOR
+  # makes openssl-sys link the runner's preinstalled system OpenSSL instead of
+  # recompiling the vendored copy (matches the documented local build).
+  OPENSSL_NO_VENDOR: '1'
+jobs:
+  rust:
+    name: build · test · clippy
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    strategy:
+      fail-fast: false
+      matrix:
+        crate: [robot-repo-automaton, shared-context, dashboard]
+    defaults:
+      run:
+        working-directory: ${{ matrix.crate }}
+    steps:
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+      - name: Ensure clippy + rustfmt components
+        run: rustup component add clippy rustfmt
+      - name: Build (all targets)
+        run: cargo build --all-targets --verbose
+      - name: Test
+        run: cargo test --verbose
+      - name: Clippy (deny warnings)
+        run: cargo clippy --all-targets -- -D warnings
+      - name: Rustfmt check (informational)
+        # Pre-existing formatting drift is not yet gated; surfaced here so it
+        # stays visible without blocking. Flip to a hard gate after a dedicated
+        # `cargo fmt` pass lands.
+        run: cargo fmt --check
+        continue-on-error: true