docs: align install and config guidance (#16)

[bigduu]

Summary

• repair Bamboo repository and issue links and update operator examples to port 9562
• distinguish the signed Bamboo plugin bundle from standalone release binaries
• document the current install command, service config path, and release-template manifest boundary
• replace the incorrect enforced-0600 claim with the actual warning-only behavior and remove speculative future promises

Test Plan

• git diff --check
• cargo fmt --all -- --check
• cargo test --locked (193 passed)
• verify Bamboo repository/issue links and the current Magpie release
• resolve and verify the current plugin bundle and .sig URLs

Closes #16

[bigduu]

Independent exact-head agent review: APPROVE. Reviewed base b81aae3 and head 37765b3. No P0-P3 findings. The README and architecture text match the current Bamboo plugin installation/trust/lifecycle contract, Magpie config precedence and permissions, the 0.0.0 release-template manifest, and the v0.1.1 signed release assets. Bundle checksum, manifest hashes, Ed25519 signature, links, locked tests (193 passed), and all three CI platforms were independently verified. Scope remains README.md and ARCHITECTURE.md only.