chore: batch RSR compliance — SPDX headers, SHA-pin actions, forbid(unsafe_code), CODE_OF_CONDUCT, CONTRIBUTING

- Add/fix SPDX-License-Identifier headers (AGPL→PMPL where needed)
- SHA-pin all GitHub Actions to commit hashes
- Add #![forbid(unsafe_code)] to safe Rust crates
- Add CODE_OF_CONDUCT.md (Contributor Covenant v2.1)
- Add CONTRIBUTING.md (standard template)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/ci.yml

@@ -72,7 +72,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@4be9e76fd7c4901c61fb841f559994984270fce7 # stable
       - uses: Swatinem/rust-cache@779680da715d629ac1d338a641029a2f4372abb5 # v2
       - run: cargo build --release --workspace
-      - uses: actions/upload-artifact@v7
+      - uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7
         with:
           name: conative-cli
           path: target/release/conative