docs: audit LinuxDo backend knowledge base

[fannnzhang]

Summary

• Rewrite the docs/knowledge backend protocol reference to be stack-neutral and independent from the reference client implementation.
• Fill gaps found against the fluxdo v0.2.15 evidence, including topic/post response variants, notification pagination fields, upload fallbacks, repeated poll option encoding, presence handoff, MessageBus channels, LDC/CDK payload differences, reward fields, Connect stats, and bootstrap metadata.
• Remove the extra dexo reference submodule and configure fluxdo as a non-recursive reference submodule so its internal submodules are not initialized for Fire.
• Stop CI/release checkout paths from recursively initializing all submodules; required build submodules are initialized on demand by the verification script.

Verification

• ruby YAML parse for .github/workflows/*.yml
• docs/knowledge relative-link existence check
• docs/knowledge implementation-coupling keyword scan
• git diff --cached --check
• bash -n scripts/check_clean_submodules.sh
• bash -n scripts/ios/archive_release.sh

Notes

• The local working tree still has pre-existing, unstaged submodule dirtiness under references/fluxdo and third_party/openwire; those pointer/content changes are intentionally not part of this PR.